Another thing to note is how Kiku is reacting to her dating situation with Sena compared to with Yuuna. With Yuuna, Kiku was fine just casually dating and never seemed bothered enough to push the issue. She seemed just as casual about that relationship as Yuuna. In contrast, with Sena, Kiku is increasingly becoming impatient in a way that runs counter to her normal personality and even shocks her. There is a clear difference between Kiku's (platonic) relationship with Yuuna, compared to her (romantic) relationship with Sena, now. She has undeniable desires that were not shown with Yuuna.
So this series has interesting contrasts between this relationship, just as it has interesting parallels between Sena's (familial) relationship with Yuuna, and Yuuna's (familial) relationship with Kiku, where both Yuuna and Sena seemed to become confused about the types of love they felt towards someone they considered family.