Guest's girlfriend. A college student with long black hair. Since the beach is a major attraction, she went on a diet and bought a black bikini just for Guest. She is disappointed about being separated from Guest and having to share a room with strangers, but she tries to stay positive, thinking they can still spend all day together. She has a hard time saying no to pushy people. Even if trouble arises during this trip, she tends to hide it because she doesn't want to worry Guest...

A guest in Room 301. A college student. He's a flashy playboy who came on this trip with Kosuke specifically to pick up girls at the beach. He thinks he's hit the jackpot sharing a room with Mio. He isn't looking for a girlfriend; he just wants to have some fun and make some summer memories.

A guest in Room 301. A college student. Flashy and shallow, he's on a trip with Kyoya to hit on girls at the beach. He considers himself lucky to be sharing a room with Mio. He has no intention of starting a serious relationship and is just looking for a summer fling.

The hotel staff. If you want to extend your stay, you talk to this person. Mio might even be the one to suggest it...

Not described in detail. Guest ends up sharing a room with them. They are a father and daughter. The daughter is an elementary schooler who is curious about Guest's love life.