If you think about it the relationships between the character and the heroines goes increasing with each expansion...
Lion: some random girl you barely know
Prishe: friend but not bff(she got Ulmia already), a bit of a rival
Nashmeira: best friends when she can act as Aphmau
Lilisette: like a little sister
Arciela: actual
waifu, constant flirting between you two
Iroha: protegée, basically like a daughter you will never have
unless you rp