If you're looking for manga similar to Kokuen no Valkyrie, you might like these titles.
The Japanese government developed a military project where they created "Iron Princesses", schoolgirls who were altered to strengthen their body by replacing their bones with steel and artificial muscles. The Iron Princess are experts with the katana and are allowed to fight in the streets to determine the cream of the crop. Those who repair the Iron Princess are medical experts called Toui and they work to maintain and improve the girls. Sakuradamon is an academy built to train girls like Asami Honoka, an Iron Princess and Nagamitsu Yomogi, a Toui. Asami is a mysterious and powerful fighter while Yomogi is a medical child prodigy and they have to work together if they value their lives on campus.
Yui, a girl who loves panties who gets wrapped up in battles using powerful underwear. Yui receives special striped underpants that give her powers.
A clan of men and women with occult capacities were in the service of most powerful and have occupied themselves, since Antiquity, with the most difficult missions. They have now almost all disappeared. In Japan of today, a war rages between the survivors of this clan and the daughter of their ex-leader.
Ellen, the exiled queen of the country, visits a famous blacksmith in search of equipment that will allow her to fight a black dragon who destroyed her palace and kingdom. The blacksmith is not convinced and things begin to turn interesting... as he demands his rewards upfront!
"Prisoners" who committed crimes and ended their lives even though they had powers that surpassed humans. However, a “prisoner'', whose strength and beauty is recognized by God, is revived as a “warrior''. “Varanova'' is a beautiful human warrior who fights on behalf of the gods in wars caused by the gods.
Yuto has been plagued by the disappearance of his sister after he witnessed her vanish through a strange portal. Seven years later, he sees two girls emerge from the same magical doorway. Not about to let this chance to find his sister pass him by, Yuto follows them back through it and is transported to a strange and dangerous world. There Yuto finds his sister but at a price. A terrible mistake costs the lives of many of that world's inhabitants, and Yuto is to blame. Can Yuto atone for what he's done and bring his sister back home with him?