A very common schoolboy Kitsuki Tomohiro, it is attacked by the gargoyle in the world like the game. Princess knight Arisu and woman warrior Frey who fights bravely.
The reason why Tomohiro is in this fantasy world yuniforia, it is because it is summoned by Arisu and Frey. To oppose the crowd of gargoyle that approaches the king capital by a large amount, his sperm which let magical power increase drastically was necessary.
To marry when having sex even once in this world, Arisu and Frey hold the ceremony of marriage with Tomohiro, the vow of new marriage first night was exchanged.