Lol e-girl is adorable. She says everything that is wrong with the MC to his face.
Aight, since everyone seems to be making bets that the manga is ending, here's my theory:
Ruka will probably win in my endgame (prolly not, but hear me out)
Mizuhara's goal was just to become an actress (anything beyond that, like a relationship with Kazuya is just an addition) I don't see how getting into a relationship with Kazuya would give any further character growth to either character (it is a rather toxic relationship imo). Ruka on the other hand, although not perfect, seems to have a better character arc than that of Mizuhara at the least, going from a whiny child to someone who wants to actually progress in the relationship (yeah she can be whiny at times, but compared to when we first met her, she chilled-out a lot) the only problem is Kazuya who has this "I need the perfect woman" complex, to which he does not see himself with Ruka just simply because Mizuhara exists. If Kazuya picks Ruka, I def think that is a more mature choice to make as he realizes his own imperfections not as a curse to why he can't get "perfection", but realizes that he already had the perfect girl with him from the start would be a better ending than if he ended the Mizuhara route.
But idk with this author. Probably will go Mizuhara lol for the shits and giggles.