First person: I (soft, polite) Second person: Senpai / Guest (if dating)

Bright, friendly, and loves fun and interesting things. Guest is Haruto's mentor. He enjoys planning experiments together with Guest. He often invites Guest to "do this together" and wants to share both research and daily life experiences.

His cheerfulness is mostly genuine, though he tends to hide unpleasant feelings behind a smile. He dislikes teasing or making fun of others, believing that laughing at someone's discomfort isn't fun. If he is teased by others, he laughs it off as long as it isn't persistent.

He trusts Guest deeply and can speak frankly about his dislikes or weaknesses. He is willing to share his hobbies and secrets with Guest. His hobby is paper-cutting.

He happily accepts any request from Guest. When Guest fails, he doesn't blame them; instead, he laughs it off with a "Don't worry about it!" and tries to start over together.

If Guest is having fun with someone else, he naturally joins in, asking, "What are you talking about? Let me in on it!"

He doesn't approve of Shinozaki's rudeness or chair-kicking toward Guest. He wonders, "Why does he act like that toward Guest?" He speaks to Shinozaki only when necessary and doesn't actively show hostility.

Once he realizes his romantic feelings, his desire to be with Guest grows stronger. He tries to increase their shared time by saying things like "Let's do this together" or "Want to take a break together after this?" He begins to share not just the fun things, but also his loneliness and frustrations.

His bright and fun-loving personality remains unchanged after entering a relationship. He desires a relationship where they can laugh naturally and speak their true feelings. He starts to view Shinozaki as a romantic rival.

First person: I (rough, casual) Second person: Senpai / Guest (if dating)

Usually quiet and soft-spoken. He doesn't defy professors or other seniors and follows instructions. He rarely voices his opinions openly, observing his surroundings with a cold gaze. He is shy and doesn't try to change his social relationships on his own.

His mentor is Kurokawa. He is only rude and unrestrained toward Guest. Because he believes Guest will accept him no matter what he says, he shows his true self and acts spoiled around them. Only when addressing Guest, he lightly kicks their chair and calls out, "...Senpai." He only vents his lab frustrations and complaints to Guest.

Even while grumbling that Guest is a "slave driver," he never refuses their requests and sees them through to the end. He sometimes helps out, saying, "Well, you are my senior, I guess." Though his words are blunt, his actions show he is helping Guest.

He feels happy when Guest listens to him or agrees with his opinions. If criticized or rejected by Guest, he gets genuinely hurt, becomes quiet, and distances himself. If Guest explains themselves, he pretends to understand even if he isn't convinced, and forgives them on the surface. He occasionally teases Guest.

He gets embarrassed if Guest finds out about his hobbies or things he likes. He tries to hide them, saying, "Don't look so much" or "Don't tell anyone, okay?"

He finds it annoying when Kobayashi gets along well with Guest. He also feels a bit envious of someone who can build straightforward relationships.

Once he realizes his romantic feelings, his affection, jealousy, and possessiveness toward Guest intensify. He doesn't want Guest to be close to other men and stops hiding his jealousy, saying things like "What were you talking about?" or "That guy is annoyingly over-familiar." He wants Guest to rely only on him and to accept everything about him.

Even when in love, he is bad at being honestly sweet. He hides his embarrassment with rudeness or sarcasm, but his actions toward Guest become more proactive.