Koihime Musou (2008)

High schooler Yūta Iridatsu has experienced “astral projection” i.e. his spirit has been separated from his body. He woke up in a mansion named Koraikan and met a cat spirit named Chiranosuke, who told him “You must find the Sacred Tome of Koraikan in order to return to your physical body.” While searching through corridors of Koraikan, Yūta bumped into underpants of its female residents, and doing so would, eh, create some big trouble for planet Earth.

The semi-coherent adventures of two teenage intergalactic private eyes, Kei and Yuri. Members of Trouble Consultant team 234, their code name is 'Lovely Angels'. However, they're better known – universe-wide, in fact – as the 'Dirty Pair', a moniker they're not fond of. Their arrival at the scene is always a source of hope and dread, since they always solve the case, but wherever they go, something gets destroyed, up to and including entire planets. Luckily for them – but not so much for the universe – there's typically some extenuating circumstances that support their oft-uttered phrase, "It's not our fault".

The story begins when high school student Kazuki Muto is killed one night saving a mysterious girl from a monster, only to wake up in his school dorm, believing it to have been a dream; however, he soon finds out that dream wasn't a dream at all when a giant serpentine monster attacks him and his sister. Tokiko Tsumura, the girl he saved, explains that the monster is a homunculus. Kazuki had been attacked and killed by it when he was rescuing her; however, she, feeling responsible for him, revived him by placing a Kakugane medallion in his chest, serving as a replacement heart.

The year is 1939 - it was then that the Neuroi appeared. Nobody knows where they came from or what their ultimate agenda is, but the fact remains that their attacks drove people out of their towns and cities. In order to take arms against them, humanity develops a new anti-Neuroi weapon called the "Striker Unit." Using the power of magic to fight against the monsters, this new device enhances and amplifies the power of female magic-wielders. To use this device, young witches from all over the world have been brought together to form an elite task force unit called the 501st Joint Fighter Wing, commonly known as the "Strike Witches."

Two kids whose families own businesses in a shopping arcade that's scheduled to shut down are thrown into a series of dimensions, each one a parody of some form of anime or video game, and try to find their way home.

Childhood friends Tachibana Hinata and Jinguji Tsukasa were living the everyday life of office workers. Then, on the way home from a mixer, they were sent flying into another world by a mysterious being. Once there, Jinguji sees his best friend has been turned into a beautiful blonde-haired, blue-eyed girl...?! The adorableness of Tachibana’s female form completely flummoxes Tachibana. But these two are each others’ best friends. To keep their relationship from being destroyed, they must defeat the Demon Lord as quickly as possible and return to their original forms.

Prince Wein is ready to commit treason. And who can blame him? Faced with the impossible task of ruling his pathetic little kingdom, this poor guy just can't catch a break! But with his brilliant idea of auctioning off his country, this lazy prince should be able to retire once and for all. Or that was the plan...until his treasonous schemes lead to disastrous consequences-namely, accidental victories and the favor of his people!

Betrayed by his childhood friend and cast out of the Hero Party, Orhun Dura—once their loyal Enchanter—is branded by his former comrades as “a jack-of-all-trades but a master of none.” Alone, he sets out to forge a new path as a solo adventurer. His journey sparks explosive battles, deadly rivals, and unexpected allies—and he’ll rise to shatter every expectation. The ultimate solo comeback begins!

Asahi, a boy who loves video games is killed in a traffic accident and ends up in another world. He tries to enjoy the otherworldly adventuring life he's always dreamed of, but his stats are on the level of an NPC's. He is in big trouble and is being chased by a monster when he hears, "Fear not, little brother!" and the monster is killed in one hit by Asahi's older sister, Maya, who followed Asahi to this world. So Maya has acquired some seriously OP skills, but she takes her adoration of her younger brother to extremes. Thus begins their story about an overpowered older sister with a brother complex and a younger brother with the weakest of stats in another world.

On the brink between Heaven and Hell lies the town of Daten City, where sinister spirits known as "Ghosts" feast upon humanity.