Gin is a spirit of the forest. He encounters Hotaru first when she was very young and got lost in the forest. After helping her out of the forest, Hotaru stated that she will return to give him a gift. From then on, the two became close friends and met each other every summer.

Spoiler

Gin was once a human, but died from being abandoned in the forest as a young baby. The mountain god cast a spell on Gin, allowing him to live. But since the spell casted upon him was fragile, if he ever touches the skin of a living human, the spell would break and he would disappear.