Strange Mansion

Sadashima fell in love with a handsome senpai while she was in high school, but didn't have the guts to tell him before he graduated and moved away. When Sadashima graduates the next year, she follows her senpai, Shirahai, to Tokyo and manages to move in next door. She totally believes that the two of them can now hook up, and can't wait to knock on his door to 'coincidentally" find themselves neighbors.

She's flabbergasted to find a woman answering Shirahai's door, and then blown away to find out the woman is Shirahai! He's had a sex change!