He's heavily featured during the story, but only fought during the final mission.
Shu possesses supernatural powers, the most notable is the ability to summon fire out of nothing. Given the timeframe of the story, it's not known if it's a product of the Tenma Mirrors' magic or if it is Shu's own power, but no other characters, Fuka or otherwise, seem to be capable of the same. He also has a minor form of telekinesis, creating a damaging shockwave around him; this shockwave produces a purple mist, similar to Nagi's kawarimi, so it may have the same origin.
During the final battle he uses a duplicate of himself to trick Zen. This duplicate seems to have been created with the Tenma Mirrors, similar to Kaede, but lacking the identity loss of the latter. While not as strong as the real Shu, the duplicate can still use many of his abilities and is strong enough to defeat Kaede and put up a fight with Zen.
Shu is also a master of Fuka ninjutsu and kenjutsu, and unlike his fellow clansmen he conceals his weapon in a shikomizue; said sword is roughly the same size and shape as a ninjato, and used in the same manner.
His superior abilities may have also played a factor in the destruction of the Fuka clan, considering only he and Nagi played a part in it.
Zen and Shu were apparently close friends before the events of the game. While there's not much evidence of it, it was enough for Shu to share his desire for peaceful retirement with Zen, even if he didn't follow through with it. They worked together for many years as houseguard of the Hojo Clan, which is how they met Sakuya. Despite this, Shu didn't show any regret for destroying their mutual home, killing San, and leaving Zen for dead. During the final battle, in the Two Flowers route, Shu tries to kill Kaede because "it must be painful for Zen (that Kaede can never be San)", and confesses both his goal and motivations to Zen when confronted on them. This behavior is most possibly a remnant of their broken friendship.
Nagi is Shu's accomplice and confidant. Despite this, Nagi's words hint that Shu resents her for not being able to save Shizuku's life. Their interaction is minimal in the story, and whenever together Shu seems to regard her coldly. However, when Nagi is slain by Zen, Shu buries her in a makeshift grave, so he's not as callous to her as it seems.
Shu loved Shizuku, and his affection was equally reciprocated. Her death drove him to despair, and served as a catalyst for Shu, who already held contempt for war, to take extremely drastic measures to end war definitely. His mourning heavily influences his interactions with other characters, in particular Zen and Kaede, whose motivations and states of mind somewhat reflect his own.
Shu used to be childhood friends with San, but the nature of their relationship before the events of the game is not detailed. Shu let Nagi kill San on the bridge of the Fuka Village, then he himself burned her body, and never in the story does he seem to regret it, but unlike Nagi he never ridicules San's memory. During the final battle, he unfavorably compares San to Kaede, based on Zen being incapable of loving the latter as he did the former.
Shu only meets Kaede during the final battle, in the Two Flowers or One Flower route. He tries to kill Kaede in an misguided attempt to spare Zen's feelings, as in his own words "it must be painful for Zen (that Kaede can never be San)". However, he seems somewhat sympathetic to Kaede, mostly because he sees her dedication to Zen as a reflection of his lost love.
Shu used to be a houseguard of the Hojo Clan, which is how he met and befriended Sakuya. Their relationship was close enough for Sakuya to blindly trust him, but at the time of the story Sakuya has become nothing more than a pawn for Shu, who kidnaps her from her home and tricks her into believing it to be the wishes of her father. As he took her to Kazama, allegedly an ally of Hojo, he might have intended for Sakuya to suffer no harm, but he also didn't make any effort to protect her.
Ichijo, Kazama & Kihan Edit
Shu manipulates the three warlords of Utakata with false promises, and all three of them seem to trust him. It's clear from the start that his words are empty promises, and that he only tricks them with the intent of letting the war draw longer.
- In concept art he carries a staff with what appears to be mummyfied human remains. This was changed for the character render.
- The scar in his abdomen was from a past attempt at using his own kidney in hopes of reviving Shizuku.
- The Cypress tree is known as a symbol of mourning. They are often planted in graves or places considered 'haunted'. Fittingly, death is a constant in Shu's past and motivations.
- He's the only known Fuka not named after a flower.
- His design, role as main antagonist, supernatural powers and conection to the Tenma Mirrors draw similarities to Gamuran from the first game.
- He is playable as an alternate skin for Zen.