Shaman's Sanctuary -Miko no Seiiki-

You play as Mafune Itsuki, an ordinary guy visiting his tsundere childhood friend Hino Mizuno, who is a respected priestess and wants Itsuki to crossdress and join her temple as a "god". He healed Mizuno once thanks to his secret powers, and she wants him to use them again. But, if Itsuki uses them in a battle with Mizuno as his partner, there'll be some perverted consequences... Post-war Japan makes religion a mandatory part of education to heal those with wounded hearts. A few decades later, Japan is 99% religious with many different religions, some of which cause problems with their illegal recruitment of followers. The government decides to unite all the religions by selecting the ‘god amongst gods’. Itsuki has the power to heal injured people. His childhood friend Mizuno knows about his special ability since he saved her in the past and she persuades him to join the battle. Itsuki summons protection mikos to battle with mikos from other religions. However, there is an unusual side effect where he gets sexually aroused when he uses his powers.