In all the female character polls I've seen, men always pick the female characters who either have a gap moe or are major teasers like Yae. Even if it's a girl with a more brutal playstyle like Mavuika's, she'll be afraid of ghosts, have girly hobbies or something like that. I think Ei is a good example of this with how soft spoken she can be and via her love for sweets and dango milk. But then again, this is my impression as a yume.