If you're looking for manga similar to Shin Ikkitousen, you might like these titles.
A shy, bashful, and nervous girl tries to survive in a high school for delinquents.
Follows Mio Amasato, a high school girl who controls a bizarre mechanical doll.
When forcibly injected with the DNA of Musashi—the legendary swordsman—by the secret organization Akai Umi (Red Sea), Hagane Yakushimaru becomes a master fencer with supernatural powers. She sets off to rescue her parents, who have been abducted by Akai Umi, making friends and foes with supernatural beings (parasite projects) who have also been injected with the DNA of other historical figures. What is Hagane's secret? Why is she the only successful female DNA injection recipient? What exactly is the project called the "Revelations of the New Millennium"?
This is a tale of modern-day magical ninjas. Reito is just an ordinary guy, who wants to maximize his own happiness by being cool and not thinking of others. However, his stupid, annoying, large-breasted neighbor Iona Shiragami keeps trying to be his friend. One day, he learns her secret: she's a ninja who guards a powerful family ninja art, and other ninja are here to take it from her. When Reito is killed in the crossfire, she uses her magical ninja art to bring him back. However, the art also turns him into a super powerful monster. Will he be able to turn back to how he was before, and what will become of his life now?
Shuichi Kagaya an ordinary high school kid in a boring little town. But when a beautiful classmate is caught in a warehouse fire, he discovers a mysterious power: He can transform into a furry dog with an oversized revolver and a zipper down his back. He saves the girl's life, sharing his secret with her. But she's searching for the sister who killed her family, and she doesn't care how degrading it gets: She will use Shuichi to accomplish her mission...
Ageki Kyousuke, a fat guy with a big appetite, has always been interested in Mitsukura Itsuha, a girl who doesn't stand out in his class. He comes across her alone on the rooftop after school, exposing her erotic body in an extreme swimsuit! Kyousuke finds out Itsuha's secret, which is too unexpected to be ......!
In order to determine which hot spring is to be the top overall, all of the hot springs within the region enter an unofficial tournament. The tournament is simple battle of capturing the enemy's flag, but the battle itself goes beyond any human measure. It is customary for a female to enter these battles. Carrying their pride and their flag, their only objective is to defeat their opponent. Hence they are commonly called "Fighting Spring Princesses." Kikko, the Fighting Spring Princess of the Aizen Hot Spring Temple, is an eccentric, hot-blooded person who is going to have her debut battle.
In the land of Gion, the capital of Japan, a mysterious "divine power" has brought about great prosperity. It is a power that only brings about changes in girls in the form of turning them half-animal, a sign that they are servants to a god, as well as granting them great power. Some that are strong enough become Onmyou and fight evil. Others whose power have gone berserk become Orochi, fated to bring death and destruction to man. It was once thought that those who became Orochi had to be slain with no hope of saving the helpless victim—until a mysterious young man named Gion appeared to save one such girl. Will he be strong enough to fight the Orochi and bring an end to their terror?!