妹系巨乳の親友が彼女のいる俺を誘惑してきた

One day, Hiro received a request from Yui, a friend of his girlfriend Akari. Her request was all about letting her be his "girlfriend" for just one day. He refuses because he doesn't want to betray Akari, but Yui's seduction leads him around by the nose, following his lust... (Source: Melonbooks, translated) Released at Comiket 99.