Coffin Boy is the eleventh chapter of the Servamp manga series.
The chapter begins with Mahiru narrating, revealing that school is almost over and that summer starts in three days. While at school, Koyuki and a few other students are feeding Kuro, who is in his cat form. Mahiru gets annoyed at his classmates giving Kuro this attention and states that he is going to get a drink and pulls Kuro along with him to the bathroom.
Once inside a stall secluded from others, Mahiru tells Kuro to stop with the cute kitten act because he is afraid someone may find out he's actually a vampire. He is also afraid of other vampires being near by without them knowing. Kuro transforms to his human appearance and tells Mahiru that the girls love him and not to be jealous. Mahiru insists that he is not jealous and tells Kuro to eat lunch in his bag instead in front of others while at school. Kuro says that he already has and turns back into a cat and tells Mahiru to pet him because it will make him feel better.
Mahiru begins talking about how Tsubaki's subclass can blend in with humans and could be anywhere so they should be careful. Kuro tells Mahiru to relax and that everything will be okay. Mahiru is still worried.
From outside their stall, Mahiru and Kuro suddenly hear a voice talking, saying to someone that they need more information and that Operation Sleepy Ash is "a-okay". The two people begin to leave the restroom and Mahiru and Kuro follow them out. Mahiru searches the halls for who it could have been, suspecting them to be vampires.
Mahiru sets his sights on someone, believing him to be one of the people he heard. Suddenly, the person slips down a flight of stairs and Mahiru rushes to help him. Kuro tells Mahiru that he is too trusting. As Mahiru approaches the stranger, the other suddenly gets milk spilled over his head, and a soccer ball follows, bouncing off of him. The other student sighs and remarks that he expected those events. He states that his motto is "Always be prepared" so he brought a towel and a cold compress. He says that disasters are no big deal if you're prepared and Mahiru is baffled by this.
The student addresses Mahiru and introduces himself as Tsuyuki Shuhei, student council vice president. He tells Mahiru that they need to talk about his culture festival "broom trick". Mahiru is panicked to remember of when he jumped off the roof after Sakuya and used his lead and is worried that people saw him do this. Tsuyuki gives Mahiru a volunteer form for the summer festival as a punishment for breaking the rules. Mahiru realizes that this punishment means he will miss training with Mikuni. Mahiru still anxiously wonders if the other is a vampire. Tsuyuki begins to leave, but Mahiru stops him by pulling his shirt sleeve and accidentally ripping it. Mahiru offers to sew it back together. As he does this, Mahiru bluntly asks him if he is a vampire.
The scene cuts to Mahiru on the phone with Mikuni, who is amused that Mahiru simply asked Tsuyuki that question. Mikuni asks what Tsuyuki said in return, but Mahiru says he said nothing much. Mikuni says that Tsuyuki sounds strange and says they can train later. He also tells Mahiru that maybe he will come to the festival. Mahiru tells him that this is serious. Mikuni says he could size up the crowd and the vice president. He then thinks if he should leave Jeje behind when if goes. Mikuni is then shown leaning against the wall while Jeje kills a vampire. Mikuni takes back his idea, saying it's mean and that Jeje can come so he can tease him. Mikuni then begins taunting Jeje by asking him if he wants some blood. Jeje gets angry and starts shooting at Mikuni. Mikuni laughs and hangs up while Mahiru thinks to himself that Mikuni is an idiot.
At the festival, Mahiru's punishment is directing cars. A car pulls up and he directs it to the parking lot. He then realizes that the driver is Misono's driver, Dodo. Dodo says that the kids want snacks and that the parking lot is so far. Mahiru tells him to wait and that he will get everything for them. Mahiru comes back with arms full of snacks, exhausted from rushing. Dodo thanks him and drives off. Mahiru is then shown working hard for the other guests at the festival.
Kuro tells Mahiru that he always gives 110% and that it's almost time for fireworks, so their area will clear out soon. Mahiru begins saying that the festival was not a trap, so Tsuyuki is not a vampire, just a normal student council vice president. Kuro tells Mahiru that paranoia isn't his thing, unlike Mahiru. Mahiru asks Kuro if he lazes around at school to help him relax. Kuro says that nope, being a worrywart is actually better.
A dark shadow belonging to Shamrock starts to approach the two. Shamrock gives Mahiru a briefcase and tells Mahiru that he found it. Mahiru, unaware that Shamrock is Tsubaki's subclass, accepts the item and starts heading for the lost and found. Shamrock tells him to hurry before the fireworks and walks away. Kuro tells Mahiru that he needs to stay close to his Servamp, but Mahiru tells him it's not far.
Within the crowd of the festival, a boy is looking for a lost item he describes as really big, but no one can help him. Mahiru notices this and asks if he can help. The other boy gladly accepts.
The boy tells Mahiru that he was handing out hot springs coupons and Mahiru asks what he lost. The boy tells Mahiru that he lost a big, black box and tells Mahiru it's like a coffin. Mahiru is startled by this and thinks that this situation reeks of vampire. Mahiru asks what the coffin is for and the other says it's for vampires to sleep in. Mahiru just smiles while freaking out on the inside. Mahiru wonders if the boy is a human or a vampire.
The boy asks Mahiru if he lives near by and that he knows about the vampires. He says a vampire planned a hit, so he came to stop it. Mahiru wonders how the other knows about an attack that's going to happen.
Suddenly there is an explosion and someone in the crowd said they saw it and that it was a briefcase that exploded. Mahiru realizes that he is still holding the briefcase Shamrock gave him and the boy asks Mahiru if he is the bomber. Mahiru says no and realizes the person who gave him the case is probably a vampire. Mahiru says Shamrock seemed normal and remembers what he said about hurrying before the fireworks. Mahiru looks at the time and sees that the fireworks start in one minute. Mahiru contemplates his options, which are to call Kuro, somehow get the coffin boy to help, or use his powers.
Mahiru remembers what Kuro said about paranoia not being his thing and makes a decision. Mahiru asks the coffin boy if he is a bad guy and the others responds with a confused "Nope". Mahiru says he wants to believe in him, plain and simple. Mahiru calls out for Kuro, who swoops down into the scene. Mahiru says there is a bomb in the briefcase and for Kuro to do something. He makes Kuro drink his blood and the chain connecting them appears. The coffin boy sees this and recognizes Kuro as a Servamp.
Kuro picks up Mahiru under his arm and tells him to hold on as they ascend into the sky. The coffin boy watches, amazed. Mahiru tells Kuro to throw the briefcase. Kuro does and Mahiru says that he did it too soon because there are still ten seconds before it explodes. The two fall back to the ground and hope for the best. The coffin boy suddenly catches the briefcase in a coffin a closes the cover. Mahiru tells him to run away because it is about to explode. The boy tells Mahiru not to worry because nothing will destroy his coffin.
Shamrock is then shown on top of a telephone pole laughing and talking to Tsubaki, who is sitting on a nearby roof. He calls Tsubaki "Young Master" and asks if he saw that. He continues, saying their funeral service is open for business. Tsubaki chuckles and smirks, asking if they should now play with the world as fireworks go off.
Back to festival, the coffin boy is shown next to a large coffin with the writing "Visit Shiranoba Hot Springs" on it. The coffin has smoke from the bomb emerging from it. Mahiru and Kuro are confused. The coffin boy says that he found his coffin and thanks Mahiru. Mahiru asks who he is. The coffin boy introduces himself as Sendagaya Tetsu, hot springs heir. This does not ease the Sloth Pair's confusion.
The coffin slowly begins to creak open and a voice inside calls Tetsu an idiot and asks how he could leave him. Something burnt plops out of the coffin and Tetsu says he forgot about him. He tells Mahiru and Kuro to relax, he's okay. Kuro sees the charred bat on the ground and says "Long time no see". The bat is then introduced as Old Child, the Servamp of Pride.