Naruto System in One Piece - Chapter 461: The Wager

Xueyue's life was filled with nothing but unfortunate events. Her mother died giving birth to her, her father abandoned her for another family, her stepsister stole her beloved, and she was framed for a murder she didn't commit.
Sentenced to death by beating, Xueyue thought her horrible life would finally end.

Luo Ling, an expert in the art of disguise, was bound to a System and was eager to begin his task.

As a result, before even successfully completing a mission, he got married!

At a 36 degree angle, Luo Ling sorrowfully looked up into space: “Tong’er, tell me, do I still have a chance to free myself?”

System: “… Your man is behind you.”

Luo Ling: “!!!”

The person who arrived, gathered Luo Ling in his arms, hugging him from behind as he said in a bewitchingly dangerous tone: “Based on your thoughts, it seems that I have not given you enough love. So let’s proceed in exploring ways to continue a new life.”

- Description from Novelupdates

Lin Wanwan is a pitiful mentally-disabled girl. Not only does she suffer abuse from her stepmother, her stepmother even attempts to use her as a sexual commodity to pleasure others. Eventually, the poor Wanwan dies from an overdose…

Zhang Xuan traverses into a foreign world and becomes an honorable teacher. A mysterious library appears in his mind. As long as it is something he has seen, regardless of whether it is a human or an object, a book on its weakness would be automatically compiled. Thus, he became formidable.

“Emperor Haotian, why don’t you like to wear underwear? To think that you’re still an emperor, can you pay more attention to your image?”

“Fairy Linglong, if you continue to suffer from insomnia, you can always look for me. I have a way with lullabies!”

“You as well, Qiankun Demon Lord, can you cut down on the garlic? Do you want to stink me to death?”

…

This is an incredible story about the heritage between teacher and students, cultivating and guiding the world’s strongest experts.