ふたば☆ちゃんねる3

The latest title in the Futaba☆Channel series by Yumemisou. Itsuki was spending his summer vacation doing nothing at his house when one day he found himself turned into a girl thanks to a bar of soap that his osananjimi Mii was carrying. She was delighted that it worked and wanted him to play with her for one day. He agreed, thinking that she knew a way to turn him back. However, nothing happened and his summer vacation of chaos has begun.

[Taken from Micchi's blogpost]