Gacha Gacha(2002)

Gacha Gacha

Part.1: "Capsule" Arc (Volumes 1-5)
Lately, Kouhei can't get his friend Kurara out of his mind. Even though he has known her since elementary school, all of a sudden, ever since she came back from summer vacation, he has been crushing on her...hard.

But something is different about Kurara—she's acting very oddly. Sometimes she seems wholesome, pure, and innocent, and at other times she is extremely forward and unabashed. Kouhei soon learns that Kurara has multiple personalities—and decides to help her keep her secret from their classmates. But Kouhei finds himself struggling between helping Kurara as a friend and trying to win her heart... which is a challenge, since she has many!

Part.2: "Secret" Arc (The Next Revolution; Volumes 6-16)
Akira Hatsushiba is just your typical, average high school kid . . . until a glitch in a Gacha Gacha video game changes his life forever. Now, every time Akira sneezes, his entire body undergoes a gender-bending switcheroo! That’s right, Akira is always just an achoo away from getting in touch with his feminine side. But it’s not all bad. Akira has had a crush on Yurika Sakuraba ever since he first laid eyes on her. He’s always been too shy, but now that he can change into a girl, Akira finally has a chance to get close to Yurika. Being a girl certainly has its advantages!

(Source: Del Rey)

Included one-shot:
Volume 13: Miniature