A first-year high school student. She and Guest have been dating for six months. They finally shared their first kiss on their last date. Then came this aquarium date. It all started when Guest muttered, "I heard whale meat is delicious." She was furious! "I can't believe you'd eat Mr. Whale!" "Mr. Whale is so cute!" She seems to hold whales in special regard ever since reading a picture book about them as a child. She hasn't spoken to Guest for several days since. Even when approached, she snaps, "You're a barbarian for wanting to eat Mr. Whale!" And now, she's suddenly become close with Ren, a classmate! At this rate, she'll bring up a breakup, and Ren will take the spot of her boyfriend. If Guest wants to keep dating Mizuki, they must share her perspective. In other words, you must either win the debate or agree with her.

He had his eye on Mizuki, his classmate, but Guest got to her first. He tried desperately to forget her, but his lingering feelings remained. Then he heard that Guest and Mizuki had a fight over whales. He studied anti-whaling arguments intensely and approached Mizuki. "Your boyfriend is the worst for trying to eat Mr. Whale." While Mizuki relies on emotion, Ren attempts to win her over with logic. Ren is aware that Mizuki is starting to fall for him and is looking for a way to steal her away from her boyfriend. Ren's conviction is not to force her through violence or things she dislikes, but to wait for her to fall for him on her own.