Saikyou No Chikara Wo Te Ni Ireta Kawari Ni Onna No Ko Ni Narimashita – Onna Dake No Party Ni Boku Ga Haitte Mo Iwakan Ga Nai No Wa Komarun Desuga

B-Rank adventurer Rain(?) had the good luck of finding an Ancient Class item in a dungeon he snuck into. If he sells it, he can have a comfortable retired life! But the joy was brief because due to the item's effects: Rain obtained power equal to that of an S-Rank adventurer and a "Girl's Body"! Furthermore, before he even gets the chance to feel depressed, a certain incident leads to Rain(?) being invited to [Crimson Heaven], a party with only female members. Will Rain ever be able to return to his original form and take back his peace!?