"Power doesn't matter much...but ignorance makes you weak. I keep to myself and come out on top."
Syuhei Tsuyuki, also spelled as Shuhei, is a character who works for C3.
When Tsuyuki was in high school, Mikuni was his senpai. He says that Mikuni has always annoyed him, even since then.
Izuna tells Mahiru that Tsuyuki's Father was in C3 but was killed by a vampire, it is implied this vampire is Shamrock. She says that he stills holds a grudge. His father used to work with Shamrock while in C3 and Syuhei met him when he was younger, but until recently he appears to have forgotten this.
Tsuyuki appears when Mahiru and Kuro follow him out of a bathroom because they suspect him to be a vampire. Tsuyuki then falls down a flight of stairs and has milk spilled over him and a ball hit him. He sighs and says he is prepared for disasters, so he pulls out a towel and a cold compress. He then acknowledges Mahiru and identifies himself and his student council vice president. He gives Mahiru a punishment for flying on his Lead, which Tsuyuki believes is a stunt for the culture festival. Mahiru then accidentally rips Tsuyuki's sleeve and offers to mend it. While he does that, Mahiru asks Tsuyuki if he is a vampire. While talking to Mikuni about it, Mahiru says he didn't say much.
At C3, Mahiru wakes up alone after being knocked unconscious by a stun gun that Izuna uses on him. He questions where he is and where Kuro is. He sees Tsuyuki sitting in a chair reading and accuses him of being one of Tsubaki's subclass. Tsuyuki tells him that he is his ally and that "we", meaning C3, only want to talk to him.
Tsuyuki gives Mahiru food he bought for him and tells him that he is actually not a high school student, but 22 years old and an adult.
Tsuyuki tells Mahiru that C3 wants his and Kuro's help to stop Tsubaki. He explains that C3 promotes peace and harmony, and that Tsubaki gets in the way of their mission. Mahiru says he knows nothing about C3 so he can't decide. He asks where Kuro is, believing they should make a decision together and Tsuyuki tells him Kuro is in another room.
Tsuyuki says that capturing Tsubaki is C3's main goal and that C3 once owned Tsubaki as a Servamp. He adds that it was before he started working there and that he read it in the records. Mahiru asks him when Tsubaki was there, but Tsuyuki doesn't answer him and steers the conversation back to Mahiru's answer.
Tsuyuki says that they must break Tsubaki's gang. Mahiru says if that means he must kill them, he can count him out. He says this because Sakuya is one of Tsubaki's subclass and he wants to help him. Tsuyuki says that Mahiru is being selfish and that C3 does not care about his feelings.
Tsuyuki says if that is Mahiru's final answer, he can leave. Mahiru is puzzled because he cannot find the exit and Kuro is not with him. Tsuyuki says that he is on his own to find Kuro and get out. He tells Mahiru that there are 52 doors and that Kuro is behind one of them. At this time, Mahiru begins to feel the side effects of being away from his servamp for more than 6 hours. Tsuyuki tells him that he has 17 hours, 58 minutes, and 19 seconds left before 24 hours pass. Mahiru still refuses to work with him and begins trying to find an exit himself. Tsuyuki counts down time for Mahiru by reading.
Mahiru finally escapes by using his Lead to make a hole in the ceiling then heads to the records in data room #21.
Tsuyuki makes his way to where Mahiru is and shoots a bullet into the paper he is holding. He tells Mahiru to put it down and walk away before slipping on a piece of paper and falling to the ground. Since he is always prepared, he applies an ice pack to himself. Mahiru asks him if the bombings at his school were somehow related to C3, but Tsuyuki doesn't give him a straight answer.
Tsuyuki is then scared by Kuro and says that all vampires must be broken, not just Tsubaki.
After Mahiru tells him that vampires are his friends and that he just wants to save everyone, Tsuyuki wonders if vampires can change and if they can save C3. Tsuyuki tells Mahiru that he is strange, but he almost feels that he can trust him.
Collapse of C3
While Tsubaki's subclass attempt to escape C3 as it is collapsing, Shamrock heads to a control room on the third floor. Syuhei finds him communicating with Higan and shoots at the vampire, missing. Syuhei identifies Shamrock as a former member of C3 due to Shamrock's knowledge of the system. Shamrock then tell Syuhei that he looks just like his father and thanks Tsubaki for an opportunity to kill him "again", referring to his father. Syuhei tells Shamrock he will kill him.
- Physical Strength: 5/10
- Tactics: 8/10
- Spirit of Cooperation: 7/10
- Mental: 3/10
- Outward Appearance: 4/10
- Luck: 0/10
During his confrontation with Shamrock it is revealed Syuhei has a power in his eyes that he inherited from his father, Yoshimasa; Shamrock referred to it as Hawkeye. In Chapter 62 it is revealed that Hawkeye allows the wielder to see everything in a 10 kilometer radius with a bird's-eye point of view.
Four and Twenty Blackbirds:
Also during his confrontation with Shamrock, Syuhei is shown to be able to cast a spell, "Four and Twenty Blackbirds." "Nobody in the Rye", which causes floating numbers to appear in front of him. Syuhei appears to be able to control and manipulate these numbers at will and uses them to attack Shamrock.
- While he is teased for having a "baby face", he is indifferent and calls it an "asset".
- He appears to have inherited this trait from his father, as Shamrock used to tease Yoshimasa for having a baby face as well.
- He loves uniforms.
- According to the fan book, his favorite drink is black coffee.
- He is always prepared for any situation. So much that his motto is "Be prepared".
- The members of C3 play games to see who buys them all lunch and Syuhei always loses.
- He hates vampires.
- Syuhei’s father was in C3 and occasionally took care of Tsurugi. His father was killed by Shamrock.
- He fantasizes about being on the combat team of C3, but due to his bad fighting style, he is stuck with the research team.
- In the first popularity poll he came fifteenth with 150 votes.
- According to the fan book, his personal parameter is "having luck" where he scores 0/10.
- His best parameter is "tactics" where he scores 8/10.
- In omakes it's shown he often gets requests from Mikuni, such as bringing him coffee. However, some are absurd and he flat out rejects them, in one case Mikuni asked him to crossdress and deliver him pizza.
- His original hair color is black, but he dyed it after his fathers death, due to the fact that he looked too much like him.
- He is childhood friends with Izuna Nobel, more commonly known as Tinker.