Our heroine is girl named Hina-chan. She is in her 20s. Hina has a handsome boyfriend now, but she will always remember her first love, a boy named Itsuki. When other kids would tease Hina, calling her ugly, Itsuki would defend her, and try to cheer her up and make her feel better. He and some of his family eventually moved away, leaving Hina heartbroken. But the memory of her first love will always make Hina feel nostalgic and happy inside. Itsuki’s grandmother still lives next door to Hina, so she still has a connection to him, somehow.

One day, Hina has a dream of Itsuki, and she is feeling especially nostalgic about him. She is just mentioning her dream to his grandmother, when they are interrupted by the arrival of a stranger. It is a tall, beautiful woman. Wait a minute… it’s Itsuki! Itsuki is not joking, either. She explains that she is really a woman on the inside, and now she is dressing that way on the outside.

Hina finds herself falling in love with Itsuki, regardless of Itsuki's gender. But Itsuki is only attracted to men. Will Hina end up heartbroken all over again?

From MangaHelpers:
Tsutsui Hikari is an otaku, and he mostly avoids social life. Hikari has only one friend at school, who is also a social misfit, and he is mocked brutally by most of his classmates for being creepy and weird. One day, he ends up having to clean the school pool with Igarashi Iroha, who appears to be pretty much everything he hates in real-life girls. She skips school, has a blunt manner, doesn't have female friends, and seems the sort to be promiscuous. However, she is friendly to Hikari, and even stands up to the people who make fun of him. Hikari's bitterness and trust issues lead him to say pretty harsh things to Iroha, but she never dismisses him as creepy. After a while, it starts to look like Iroha may become his first real-life, 3D girlfriend! Will he be able to handle it?