Tetsuro in canon
Tetsuro was, according to the 2005 TV series, the first person to come into contact with the Guyver after it had been blown out to the lake shore by a grenade. Being a geek, he was fascinated by the Unit, though he was completely unaware of the large role it would play in his and Sho's lives. His first guesses about the nature of the Unit - a mecha and a tiny UFO- reflected his own interests, but would ultimately prove to be untrue.
His first guess, however, was much closer to the mark than he knew at the time.
When the Unit was triggered - by Sho tripping and falling into it in the 12 part OAV, Sho deciding to examine it closer and accidentally tripping the Control Medal in the manga, and by Sho trying to wrestle it out of Tetsuro's hands in the TV series - Tetsuro's initial worry was that it might be a land-mine, and he was scared for both his and Sho's lives.
Tetsuro in the Manga/12 part OAV
We are first introduced to Tetsuro as he and Sho are leaving school; Tetsuro expresses concern about his sister, leaving Sho to reassure him that she's fine, merely taking care of some unspecified errands with friends. Noting that it had been some time since they had done so, Tetsuro suggested that he and Sho take a rout through what he called a swamp. However, in the art depicting the area, it seems more akin to a lakeside forest than anything else.
Pausing beside the lake for reasons known only to themselves, Tetsuro began to gently tease Sho about his possible relationship with Mizuki.
Before Sho could offer more than an embarrassed, token protest, an explosion from somewhere behind them - off a ways in the forest - distracted them both from their conversation. Unknown to either of the boys, this was a product of Malmot's grenade, as he made his last stand against Chronos' forces. Realizing that the explosion had come from the direction of Mt. Narisawa, Tetsuro was either unaware or too preoccupied with what he was seeing to notice the small, round, disk-shaped object that been propelled toward them by the force of the explosion.
When Sho picked it up, examining the object that had landed in front of them with a curiosity that seemed to be habitual, Tetsuro was quick to remind his friend that the object he was holding might very well be dangerous. This would prove to be true, but not at all in the way that Tetsuro had been expecting. When Sho, all unknowing, activated the Unit, Tetsuro's first thought was that it was some kind of a land-mine and that the two of them were in grave danger.
When the Unit erupted from its casing, its tentacled mass wrapping tightly around Sho, Tetsuro was too shocked by the sudden happenings to do anything but stand stock-still and watch. As armor began to form out of the mass of once-writhing tentacles, hardening into something that seemed to resemble an insect's carapace, Tetsuro seemed to regain some of his mental faculties. At least enough to call out to his friend as the half-formed creature fell into the lake before him and vanished from his sight.
Calling out to Sho, seemingly more out of desperation than any real hope of getting an answer, Tetsuro soon found himself confronted by a large, greenish, lizardlike humanoid. The quasi-human creature was accompanied by a detachment of soldiers in strange uniforms, soldiers who seemed perfectly comfortable with the presence of someone so obviously inhuman in their ranks.
Soldiers whose leader was quick to order Tetsuro's execution for the mere act of laying eyes on them.
However a strange, armored figure rose from the depths of the lake behind him. The figure - unknown to him, Sho's armored form as Guyver I - was quickly set upon by the monstrous figure. However, in spite of the clear disparity in size between the two of them - a disparity that the Troops were quick to comment on with derision due to the fact that Guyver I was the smaller of the two - Guyver I was able to quickly overpower his larger opponent, shattering the Gregole's arms irreparably.
All of the spectators, Tetsuro included, were shocked at this turn of events.
The Guyver's next action - crushing the helpless Gregole's head into pulp - caused the troops who had cornered Tetsuro to panic and flee for their lives. Tetsuro himself, startled by the sudden appearance of Guyver I and the destruction that it had wrought on the Chronos Troops, was understandably frightened when the Unit seemed to turn its attention to him. When Sho called out to him, however, Tetsuro turned back to look at the armored figure standing behind him.
He was understandably startled to hear the voice of his best friend emerging from the alien, and extremely dangerous, figure. He was more startled, however, to see the corpse of the monster that Sho had just killed rotting away and dissolving right before his eyes. When Sho, disturbed to find himself wearing strange armor and with no point of reference for what had just happened to him, panicked and caused the armor to detach and seemingly vanish into the lake in front of them, Tetsuro could only watch it go in silent shock.
Tetsuro is next seen at Sho's house, accompanied by his sister, ostensibly to help Sho recover from the mild fever he had contracted; likely as a consequence of bonding with the armor, or that was what Tetsuro supposed. When Sho displayed the artifacts of his transformation by the armor that they had encountered yesterday, he made a joke about how the markings could possibly be some kind of an infection that would spread to cover Sho's entire body given time.
Needless to say, Sho did not find his light-hearted suggestion particularly funny.
Tetsuro is next seen with Sho, at the top of the school that they both attend: Narisawa High. His thoughts still on the soldiers that had accosted them, Tetsuro proposes the idea that they had been genetically-engineered by some secret organization with some as-yet-unknown goal in mind. Unknown to them both, he was right. Sho, however, was more skeptical than his friend, who he thought was making too much of things that neither of them understood at this point.
Sho, at that point, was more concerned with the location of the strange device that he had seen sinking into the lake that day.
Once the two of them left for home, they split up, and Tetsuro was then met by a pair of Zoanoids under the guise of local law enforcement. After being brought to an abandoned, run-down building, Tetsuro found himself confronted by a group of six Zoanoids. Just as they had begun to interrogate him about his role in the Unit's disappearance, two of them heard the sounds of an uninvited observer sneaking around outside the doorway.
Dragging him inside, they quickly found Tetsuro much more cooperative than before, but as he still did not have any kind of concrete understanding of what he had seen, his assertions were dismissed. Threatening Sho more directly only prompted the other boy to willingly call upon the armor for the first time since it had bonded to him. Allowing Tetsuro to personally witness the destruction caused by the most powerful of the Unit's weapons: the Mega-Smasher.
The next day after school, Tetsuro began to hypothesize that the reason the agents they had encountered the previous day had been unable to find the Guyver was because it was stored on another plane of existance, only responding to Sho's call. Sho himself was far more concerned with the fact that Chronos still wanted the Guyver, and what lengths they would go to in order to retrieve it.
Finding that he had forgotten something rather important to him, Tetsuro was the first to be confronted by the pair of Ramotith that Lisker had dispatched ahead of him. Sho, in full armor, was quick to come to his aid, and killed the two Zoanoids without hesitation. However, they were only a prelude to what was to come.
Inspector Lisker introduced himself to them then, mocking them while at the same stating the full capabilities of the Unit in an effort to intimidate them. Tetsuro, not one to be cowed, encouraged a hesitating Sho to continue fighting even in the face of Lisker's greater experience. He, of course, was left behind while the two of them clashed, but swiftly caught up to them on foot.
By this time, their battle had moved to the roof of the school.
Watching in the same, horrified fascination as the damage that Sho had dealt to Lisker's already-damaged Control Medal caused his armor to consume him entirely, Tetsuro was forced to close his eyes as Sho destroyed the remains of the dying second Guyver. The following afternoon, Tetsuro found himself and Sho held up late printing flyers for some unspecified event, leaving Mizuki to leave with Agito.
During their walk, after a brief conversation that offered some insight into Agito's past and the circumstances that shaped him, Tetsuro and Sho are accosted by a sextet of Chronos' Combat Agents, and Sho transforms to fight them. However, once Sho had finished with them, he was then confronted by a far more powerful opponent: the Hyper Zoanoid Zerebubuth.
However, that wasn't the only thing they were forced to face; Mizuki, presumably still on her way home from school, was taken hostage by Zerebubuth as soon as he spotted her. Tetsuro, while frightened for his sister's safety, could only wait for Sho to return. When Sho returned, carrying Mizuki in his armored arms, it seems likely that the two of them spoke about what Sho had seen when Mizuki was rescued: the mysterious third Guyver.
When their next day of classes had ended, Sho and Tetsuro found that they were not remotely as done with Chronos as either one of them had hoped: a note from Chronos appeared before them, with a challenge to come to MT. Narisawa if they didn't want anyone else involved with their troubles concerning the company. Sho was quick to decide on going, and Tetsuro was quick to follow him. Neither of them wished for the other to suffer for whatever it was that the syndicate wanted with them, and so both were insistent that the other one leave.
However, the appearance of Genzo Makishima quickly silenced what arguments the two of them had been trying to put forward on the subject.
After witnessing the death of his friend at the hands of the transformed Genzo, Tetsuro is taken into custody by Chronos agents under the command of Richard Guyot. When brought before Guyot himself, Tetsuro was furious, and then horrified when the Zoalord detailed Chronos' plans for world conquest, and displayed the armies of Zoanoids they had bred for that purpose. After being locked in a cell deep within the building, Tetsuro was greeted - to his surprise and elation - by the revived form of Guyver I.
After the two of them had escaped from the cell Tetsuro was imprisoned in, Tetsuro found himself face-to-face with Guyot once again. Demanding to know just who had been responsible for the creation of humanity, if they were indeed meant to become Zoanoids, Tetsuro was informed of the existance of the beings variously referred to as the Advents, Creators or Uranus. However, not long after their conversation had started, Guyver III appeared; declaring himself an enemy of Chronos, and going by the pseudonym of Zeus, he set off the explosives he'd previously planted.
Tetsuro ends the first volume in Sho's arms, hovering over the exploding remains of the Chronos Japan building.
The next morning, when the pair of them had returned to school, Tetsuro was the one to suggest that they avoid Mizuki until they'd managed to come up with a plausible story to tell; neither of them wishing to tell her about their battle against Chronos. Both because they knew that such a thing would distress her, and because they didn't want to chance her involving herself in a situation that was more than likely to get her killed. Tetsuro, seeing Mizuki hot on their heels, suggested that the pair of them split up and meet back in the school's ground-floor archive.
Finding himself accosted by what he had at first thought to be Sho - though he found himself startled by the fact that "Sho" wasn't wearing a scrap of clothing - he found himself cornered when the creature transformed into what looked very much like one of Chronos' Zoanoids. Rescued by Guyver I, he and Guyver I quickly gave chase when the creature threw itself out a nearby wall to escape. Finding himself questioned about the fate of the Guyver's missing arm, he freely admitted that he didn't know, having been led away by Chronos' agents right after Sho had been killed.
The pair of them continued searching for the clone, eventually finding it. However, the fact that Mizuki was in the same area - putting her in danger when the creature transformed in response to the appearance of Guyver I - meant that he needed to stay with her while Guyver I dealt with the creature. Promising to explain everything later, Tetsuro asked that she not pester Sho about what had happened.
Tetsuro in the 2005 TV series
The first time Tetsuro appears in the TV series, he preparing to depart from school; after speaking to his sister, he is then approached by Natsuki, asking for his report for the Sci-fi club that the two of them run. Not having the report to present for one reason or another, he was unable to give it over. Parting company after being admonished briefly by Natsuki, Tetsuro and Sho met up to walk home together.
While the two of them talked of their potential future plans, a detachment of Zoanoids dispatched from Chronos' Japan Branch Headquarters continued searching for the Guyvers that had been previously scattered by the blast of a hand-grenade. When one of the Units came rolling to a stop before their feet, Tetsuro was the first to pick it up, curious as to just what it might have been. Sho, however, was not nearly as sanguine as his friend, thinking - correctly, as it would turn out - that the Unit they had found was a dangerous thing.
When the group of Zoanoids that had been looking for the scattered Units finally arrived in the area where he was sitting - still stunned after seeing Sho plunge into the pond with the Guyver's armor still forming around him - Tetsuro was shocked. He was, therefore, completely unprepared for when the leader of the Combat Agents - as per his standing orders from Chronos - transformed into his battleform and attempted to kill him. Frightened by the appearance of such a monstrous creature, not just a few moments after he'd seen his closest male friend plunge into the lake he was even then sitting in front of, Tetsuro froze as the Gregole advanced on him.
Tetsuro in Warrior Guyver
Tetsuro in Son of Mine ('verse)
Making his first appearance out in Agito's safehouse, Tetsuro remains one of Sho's closest friends. His role is largely that of moral support, as he possesses none of the extraordinary powers that those who stand on the front lines of humanity's war against Chronos.
When he and the other members of their group are forced to go into hiding inside Relic's Point, he quickly makes a place for himself among the research staff who have also chosen to rebel against the company. Still later, when Sho and Agito return from their seeming brush with death with another Guyver in tow, Tetsuro is swift to welcome Ryan Crouger into the place where all of his and Sho's companions have been staying.