Finding the forgotten

So there is this yaoi I read I can’t recall the name of I’m trying to find the stories I lost from my lists slowly. But anyways it basically story is where mc need living space while in college and goes to bookstore the ml is in charge gives him the room. The store he runs is also for spirits and gods;during a deal he had youth potion spilt on him making him turn to a child but back to normal around midnight. he is an ancestral god named nishi ..? He is not the owner of the body only looking after it till his descendent that looks very similar to his true form who was in a rats body after attempting suicide returned to his body. And during the time the mc grew feeling for nishi w/o knowing he was a god till later in the story. Thank you in advance if you know it .