Hikaru has black eyes with a small iris, and features short brown hair. His uniform's jacket and pants are beige, while his sneakers and belt are blue. Inside his coat contains his white hoodie, a long, red, necktie, and his black t-shirt. When Alma becomes activated, Alma enlargens himself so that he can cover Hikaru's entire right arm. During this phase, Hikaru's hair will have an orange highlight at the frontal tip, and his left eye will have a more mechanical look to it, resembling that of Alma's, while emitting an orange flame.
Hikaru has predominantly lazy personality, avoiding most tasks and is shown incapable of waking himself up. However, Hikaru also has a more thoughtful and proactive side to him, as shown when he decided to take action when Aki was in danger.
Alma: Alma is Hikaru's mecha-ude, attached to his hoodie. For the most part, Hikaru considers Alma to be an annoyance, dismissing most of what Alma says, and being forced awake by Alma's alarm clock. However, Hikaru is shown to possess a genuine level of respect for Alma on the inside, as he's shown to rely and care for Alma.
Aki: Aki is somewhat Hikaru's bodyguard. However, she only seems to protect him as Hikaru is Alma's possessor. She is shown as cold toward him as well as always keeping an eye on him, despite her cold attitude she shows some form of warmth toward Hikaru.
Yoh: Hikaru's school friend who constantly worries over him.
- Hikaru is apparently the only Host that can survive after having his mecha-ude seperated from him, even rejoining with each other after a short period of time.
- However, there is a limited distance to which the two could be seperated, as ARMS would've otherwise just taken Alma away.