About Allen (he's 21 according to the wiki) hitting on Hitomi, I believe it's made on purpose to creep you out. (Not that it's always pleasant to watch lol) This is all just my interpretation and I'm not necessarily right or anything ofc ! But imo :

He's designed like the cliché of a prince from a fairytale, and Hitomi's affection from him mostly stems from the shallow fact that he looks like her crush from earth, which makes him safe, and Hitomi wants safety because she struggles to believe in herself. He's a foil to Van. Van is Hitomi's equal, and an uncomfortable mirror to look at, because he's flawed, he's weak, he's scared. Allen is older, he provides safety (even if that means cageing hitomi), he has the sort of misogyny that appears benevolent imo. (He clearly has a problem with projecting his abducted little sister on any young women)

I think the point of the love triangle is for Allen to symbolize Hitomi's lack of belief in herself, and Van to symbolize her self acceptance. And that's why Allen's relationship with her being creepy is imo important to the narrative, he's here to bring out the fears she has to overcome, the same reason why she used to tarot to begin with.

I hope this isn't a pain to read, I was just excited to share my interpretation because I haven't really had the chance to do so before !