What were the consequences of a main character making a deal with a demon?

The way of a Demon Lord- since the beginning of time, countless demons dreamt of it but few dared to tread on it, and even fewer reached its end. But the rarest of them all were some special demons who were not allowed to step on it, because if they were to become a Demon Lord- even the other lords would have to bow their heads. Abhorred and hunted by all, they could not do anything but hide till their lifespans came to an end. But for the first time ever, one such demon chose to do otherwise. Follow Adrian Darkheart as he uses his special demonic power, superior intellect and innate brutality to walk the path of chaos and destruction and become the greatest Demon Lord ever.

Bell Cranel was rejected by every familia he tried to join until he met Hestia. In a few, he was rejected quite violently. And in one particular instance, he was thrown out and bashed his head against a wall. Well, that's apparently where I come in. Not sure how and why I'm here. Not even sure who 'I' really am at this point since Bell's memories are definitely clearer than 'mine'... But I guess we're doing this. Hopefully I've got some useful cheats. Maybe?

Damien Julian is an 18-year-old loser, who has been bullied and mistreated his entire life, at home, he has to deal with his abusive father, and at school, he is constantly been bullied by delinquents, and to make things worse he is always looked down upon by his peers, till one day a mysterious screen appear before him as it said. [The world has seen the lingering evil in your heart] [Would you like to be one of the nine demon kings of this world] [If so what are you willing to sacrifice?] In the heat of the moment, Damien made a deal with the world, that he would give up everything he owns, or do anything it wants, and in exchange, he shall be reborn as a new Demon King, and what the world required from him as payment was. [In exchange for power, become a slave of the world, and act as an anti-body for all eternity] At that moment, Damien agreed, but little did Damien know, that becoming a slave to the world meant he has to be its immune system, what that entail is, that anything that threaten the world must be destroyed even if he has to wipe out humanity, to save it, or assassinate historical figures to bring fort balance or even manipulating events that can potentially end the world, to save the world, this is the story of a necessary evil, not the story of a hero who cares for others. P.S: The Art is not mine, all credits go to the original artist

Yan Xi, a medical prodigy who obtained a doctorate at the age of 22, never expected to end up transmigrating into a novel. Her husband was the female lead's fourth brother, Gu Shen. He was a bigshot in the business world who had suffered from disability from a young age and could only move in a wheelchair. However, he was a handsome man full of schemes. Yan Xi became the cannon fodder wife of a bigshot in the business world. Her first love, Zhang Ming, had stabbed her husband's subordinate with a knife. To force Gu Shen to release Zhang Ming, she had unhesitatingly to stab herself to threaten Gu Shen. Eventually, Gu Shen released the man and gave her a large sum of money. She took this money and eloped with Zhang Ming. After that, Zhang Ming planned for a car accident that ended her life as they hit the road, which allowed Zhang Ming to conveniently take her money and run far away. When she transmigrated over, Yan Xi found out that she had just stabbed herself with a knife and was in the critical stage of deciding her future fate! Therefore, when Gu Shen threw her the divorce agreement, Yan Xi decisively refused. "Hubby, I won't divorce you." Gu Shen was surprised by her change. "Have you thought it through? I've left you some real estate and cash. It's enough for you to live comfortably for the rest of your life." Yan Xi revealed a confident smile. "I've thought it through. Zhang Ming stabbed your men with a knife. You should hand this matter over to the law. I won't interfere anymore." The surprise that Yan Xi's change brought to Gu Shen did not end there. After that, she tore off the mask of her hypocritical best friend and calmly dealt with her scheming family members. She personally treated Gu Shen's chronic illness for many years. Bit by bit, she managed to shock everyone around her who was once prejudiced against her.

Blake a guy who has been betrayed by the person who he thought, his future yet she was nothing more than a selfish bitch. After being betrayed he caught a second stage cancer, and when he thought all hope was gone all of sudden he was invited to be the administrator of a multiversal Group Chat! Where he could interact with fictional characters! Group Chat Members (Currently) : Counter Guardian EMIYA (FGO) Jaune Arc (RWBY) Satan/Lucifer (Helltaker) Echidna (Re:Zero) Disclaimer: I do not own anything aside from my OC's

"I don't have enough money or power right now, but I will definitely find a way to bring them all to their knees! I'll make them all beg!" She hissed, shaking with anger and frustration. "I will do everything, anything… to make them all regret… even if I have to sell my soul to the devil!" She said with determination flashing in her beautiful eyes. The man smirked. He lifted his fingers and tucked some errant strands of her slightly mussed up hair behind her ear. "Be careful what you wish for, Miss. A certain devil here might really fulfil your wish and claim your soul in exchange." "If that devil is really here, do introduce him to me, handsome. I would like to make a deal with him." Eva drawled out, smirking back at him.