Here is the main harem list:
Olga Discordia
Celestine Lucross
Alicia Arcturus
Prim Fiorire
Chloe
Claudia Levantine
Kaguya
Maia
Grace Campbell
Anna Florence
Mistiora Arte
Astrid Flamel
Iris Arcadia
Eleonora Bern
Kohaku
Serafina Renatus
Mel Mel
Radomira
Luca
Emilia Solva
Evelyn Moinard
Leona
Sophia van Grea
Ragnar will have romantic and sexual relationships with them. But will also have sexual relations with minor characters in Kuroinu.