If you're looking for manga similar to Joshikousei Nobunaga-chan!!, you might like these titles.
Rinko Mino, a first-year high school student, is a female manager of the volleyball club. She fell in love with her senior Yuki in the same club, worked hard at club activities, and she had a normal and enjoyable life. When she woke up one morning... She was a boy!? What will happen to the youth of Rinko, a girl who suddenly became the opposite sex!!?
Hazumu is a shy and quiet boy who loves flowers and is forced to rely on his tomboy childhood friend Tomari as a bodyguard. Yasuna is the prettiest girl in school but she avoids men like the plague… until she meets Hazumu. Encouraged, he confesses his love; heartbroken, he heads for the mountains to be with his flowers. As if Hazumu’s troubles aren’t enough, his day is further ruined when an alien ship accidentally kills him. Luckily, alien technology exists that can revive him, but not without a price: Hazumu returns from the dead, but in the form of… a cute girl?!