Synopsis

Filled with monotony and loneliness in his long life, the Demon King Lupa, sealed himself into a crystal coffin made of ice and abandoned himself into the void. He intended to stay there and sleep for all eternity.
Until one day…
[ ....Scan complete, potential host's compatibility is 100%.... proceeding to bind with the host...]
[Binding successful.]
[Congratulations dear Host! You have been chosen due to your special unique abilities! I am your newly bound Training system, Trainie! ~\(≧▽≦)/~ ]
…He was unsealed and chosen by a strange system to use his natural abilities to help repair the fragments of the system’s Lord that were scattered in different worlds.
Demon King Lupa thought that maybe his days would no longer be so dull.
Author's note: This story contains monsterf*ck scenes, and after a certain world, the MC becomes an intersex. So if neither of these are to your liking, then this story is not for you.
(Also, Trainie is a s*x training system.)