In "Kissxsis," if Kiryuu Yuuzuki hadn't entered the room, the dynamics between the characters would likely have played out quite differently. Yuuzuki often serves as a catalyst for various comedic and romantic situations, so without her presence, the focus may have shifted more towards the relationship between the main characters, Keita and his older stepsisters, Ako and Riko.
For example, without Yuuzuki's interruptions, Keita might have had