Tetsu Sendagaya first encountered Old Child when the vampire visited his family’s hot spring, drawn by the scent of Tetsu’s blood. Mistaking him for a guest, Tetsu offered a room with a view of the sun, only to block the window when Old Child explained that sunlight was harmful to him. Impressed by his straightforwardness, Old Child later chose Tetsu as his Eve, and Tetsu accepted, naming him Hugh.

During a summer festival, Tetsu misplaced his Lead, which contained Hugh inside. He met Mahiru Shirota, who offered to help search. When questioned, Tetsu openly admitted he was looking for “a coffin with a vampire in it,” shocking Mahiru. Their search was interrupted by a bomb explosion, during which Tetsu retrieved his coffin and prevented further damage by catching the bomb inside it. Recognizing Kuro as a Servamp after witnessing him drink Mahiru’s blood, Tetsu joined forces with Mahiru and Kuro, later introducing Hugh when he emerged injured. The group resolved to cooperate against Tsubaki.

Tetsu and Hugh soon joined Mahiru in training sessions under Mikuni Arisuin and Jeje. Tetsu’s blunt curiosity in handling Mikuni’s doll Abel earned him Mikuni’s disdain, but his strength proved crucial in their first challenge, where he successfully removed Jeje’s masks after receiving Hugh’s permission to fight at full power. During further sessions, he also trained alongside Misono Alicein, though he angered him by mistaking his short stature for that of an elementary school student.

In subsequent battles, Tetsu fought alongside the group against Tsubaki’s subclass, exterminating djinn and using his family’s inn as a safe base of operations. His casual nature often surfaced during tense moments, such as advertising his inn to civilians freed from djinn control. He also encountered Lily’s subclass, Yully, whom he initially mistook for a human child before learning of her true nature as a vampire.

Tetsu played a role in the conflict at the Alicein mansion, where he and his allies confronted Misono’s father, Mikado Alicein. Initially refused entry, Tetsu used force to gain access, leading to a confrontation with the family’s servants. Though injured, he continued to aid in the effort, eventually helping Misono reconcile his conflicted loyalties.

As Tsubaki’s threat escalated, Tetsu was entrusted with guarding the captured subclass Lilac. He participated in the rescue mission of Licht Jekylland Todoroki and Lawless after their capture by Tsubaki’s group. During the operation, he and Hugh confronted multiple enemies, but Hugh was ultimately trapped inside Berkia’s magic box and teleported away. Tetsu was left distraught by his disappearance and demanded answers from Tsubaki, who revealed Hugh’s defeat. Furious yet unable to stop Tsubaki, Tetsu witnessed the Servamp of Wrath’s retreat alongside Lilac, leaving him with deep frustration at his inability to protect Hugh.

Despite being only fourteen years old, Tetsu Sendagaya is frequently mistaken for a university student due to his tall stature and muscular build. He has short blond hair, often kept in place with two blue clips framing his face, and striking blue eyes. His usual attire consists of white pants, a dark blue singlet, and a white shirt with the sleeves rolled up. He also carries a blue-and-white towel marked with the hiragana character yu (ゆ), symbolizing hot springs, reflecting his work at his family’s resort.

A distinctive feature of Tetsu’s appearance is the large black coffin he carries with him. The coffin doubles as his weapon and is painted with an advertisement for his family’s hot spring business, blending his everyday life with his role as the Eve of Old Child.

Tetsu Sendagaya is generally portrayed as expressionless yet relaxed, straightforward, and simple-minded. While he openly admits that he is not particularly intelligent, his extraordinary physical strength compensates for this shortcoming. He approaches most situations with a calm and indifferent attitude, even in matters involving the Servamps and their conflicts. Unlike others who attempt to conceal their involvement with vampires, Tetsu is nonchalant about his role as an Eve, carrying his large coffin openly in public without concern.

Known for his honesty, Tetsu often speaks plainly to others, which can unintentionally come across as blunt or insulting. Despite this, he is friendly and sociable, quick to label acquaintances as friends, though this easy familiarity sometimes embarrasses those around him. His personality combines strength and simplicity, emphasizing his role as both a dependable ally and a lighthearted presence within the series.

Lead
Tetsu’s contract item, known as his Lead, takes the form of a large black coffin that he constantly carries with him. The coffin is both offensive and defensive in function, as Tetsu uses it as a blunt weapon while also relying on its indestructible nature to shield against attacks, including Jeje’s bullets. Because he is unable to make the coffin disappear, Tetsu openly carries it in public and even advertises his family’s hot spring on its exterior.

In the anime adaptation, the coffin demonstrates an additional ability: under Hugh’s command, it can release swarms of bats that attack enemies in battle.

Hugh (Old Child)
Hugh, also known as Old Child, is the Servamp of Pride and Tetsu Sendagaya’s contracted Servamp. Their partnership is depicted as unusually harmonious compared to other Eve–Servamp pairs, as they rarely come into conflict. Hugh often serves as a mentor figure, guiding Tetsu in combat and strategy, while Tetsu provides care and support for Hugh’s childlike demeanor. Their relationship is marked by mutual respect and companionship, with Tetsu frequently carrying Hugh on his shoulders during travel or battles.