Mio Yamanobe, alias Death Chronos, is a 15-year-old male student at Étoile Vio School, standing 163 cm tall and weighing 45 kg with a birthday on July 7. He possesses short grey hair styled with longer front sections obscuring his eyes and small, cat ear-like tufts sticking up on both sides, complemented by golden eyes. His attire typically features extravagant, detailed outfits emphasizing femininity.

As part of the idol unit RE:BERSERK, he positions himself as the obedient servant of Eva Armstrong, exhibiting worshipful devotion towards Eva. This devotion manifests as arrogance towards Eva's rivals and harshness towards perceived enemies. In Eva's presence, Mio adopts a childlike persona, though Eva himself remains unaware of this act. He displays open hostility towards fellow unit member Ban Jumonji, revealing a completely different personality when interacting with Ban. Mio expresses annoyance over sharing near birthdates with Ban, considers him a nuisance, and jokes about using black magic against him.

Mio's sole motivation for being an idol is his desire to stay with Eva forever, explicitly stating only Eva matters to him. His hobbies include practicing black magic, often referencing gathering sacrifices for it. He favors boiled tofu but dislikes fatty fish. His surname, Yamanobe, incorporates the characters for "mountain", "field/wilderness", and "environs/boundary", while his given name Mio means "water route" or "shipping channel".