Because out of the 5 girls, Takemoto is the only one who could actually work her way up to be together with Yuiga without other people’s help. I don’t think anyone here would disagree if I say that Yuiga has the biggest affection towards Takemoto when compared to other girls. Whether it being enough for him to fall in love is a matter of opinion, but as a male, developing a romantic feeling towards a girl who have always liked him and already having an affection to begin with is nothing short of logical (you know, like a typical childhood friend). There are numerous examples of such relationships blossomed in fictional literatures including manga, and is certainly no short of common in the real life as well. In my opinion, Yuiga can actually realize Takemoto’s feeling since the Valentine’s arc. From there on (or maybe after exam), Yuiga can actually think through their relationship by himself and realize that he actually likes Takemoto as well, instead of asking Miharu for her opinions (which I still have absolutely no idea what was even the point) and also having someone who has already passed away to tell Yuiga that he has already liked Takemoto for FIVE F*CKING YEARS without even knowing who Takemoto was.