The story revolves around Taiga, who doesn't have memories from further back than two years ago when his parents died in an accident. He lives with his sister, Tsubame, whom he finds out is from outer space with the job of protecting him as he possesses the Origin Heart.
AKANE Kotetsu
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A spirit was floating in another world's dungeon, missing its memories. Eventually "he" learned to possess other creatures and using the bodies of the beasts in the dungeon, made his way to the outside world. Dragging a young female knight, a pretty young lady, and even a beautiful mercenary into the mix, our protagonist begins his great adventure in this world.