Nice no poly
I dunno, I don't see anything that would prevent poly here.
Also, why not have all three of them be happy together?
I just prefer Honoka x Kotori & Honoka x Umi together instead of poly.
As in both of them dating Honoka at the same time but not dating each other? That'd still be poly.
If you mean enjoying the couples independent of each other, then I can understand that. I totally accept that poly's not everyone's thing lol