Kyouka Suigetsu

Main character confesses to his childhood friend. His feelings are accepted, but relations hardly progress at all, and things get uneasy. At summer roughly a year later childhood friend suddenly gets missing. Protagonist begins his own investigation and finds out that his lover is sucked into an ancient mirror by the magic of the summer festival. He starts to look into the mirror, and dreams about insult start to come to him.

[From vndbreview]