The power is Nothingness (- Redo - I Object - Remove -) basically the power that allows the MC to reject or reverse everything that happen under god control but he can't reverse or redo himself - become immortal without cultivating- And i'm planning to make about a war and there's a severe casualties and the MC reverse or say "There's nothing in this world i cannot remove, object, or redo even DEATH!" (MC) cultivation rises upon the world and struck fear upon (antagonist sect) and the world "I'll object - I'll remove - I'll redo - the surrounding 100 000km of current death!" or "I will...redo her death!" (MC's friend and his teacher name) felt fear upon the casual speaking to redo death" "don't be rash (MC name) there's ought to be something else to use, do not fight the current of TIME!" He can literally remove or redo any side effect that will probably happen Oh and another question is that...i plan to make the main character power or ability before he started cultivating to be strong AF will that be boring? Suggestion? So many suggestion Thank you! back to writing...~(^_^)~
He will lose all karma connection to any objects he reverses and that side effect will explain why only himself is immune to his power.
A good example is if he reverses a enemy's death then the villain will revive but all memories of the mc would be removed from him and all the people who knows the connection between the villain and the mc
Equivalent exchange something around MC will disappear as a price you can also make MC lose his/her memories, like a certain manhwa [author : Penguin Juice]
Maybe have your MC have to experience everything he undoes. MC gains memories of all the fear, pain, and suffering experienced during the event they undo from the people they use it on.
I would have him build up his power though some steps before getting to the the step were he can reject/reverse the laws of the world on such a large scale. If he starts with being able to reject any law at any range there is no conflict, no char growth, basically no story. start by explaining how he got the rejection power, then expand upon it. AKA have him cultivate the rejection power over your normal cultivation in the world. Tell the story of HOW he got to the point were he can reject death in a 100,000 km area, not the story of he CAN do that.
#1 worst side effect, he loses his plot armor and dies. Story ends or there is a new MC. The other side effects could be that he receives what he was trying to undo like having scars from undoing wounds. Becoming a monster or his power going haywire from reversing something corrupted. He becomes a ghost forever walking the earth for undoing someone's death or removing their ghostly goals. His power degenerates his body or soul. He could even lose his mind and become nothing more than a machine who only knows how to use the power or fight. His power makes him a different person (memory loss, blinded by hatred, madness,). Whoever he uses his power on, for some reason changes in a negative way (new personality, hates MC, madness). The power gives him pain or the pain of whatever he is trying to undo. The use of the power itself harms the world since it draws upon or destroys something essential (souls, mana, life). Turns him into a hikikomori that can only find fulfillment on a website called Novel Updates. He could be screaming about some parrot named Lord Fifth and eternal life or dragons that are invisible. The possibilities are endless you know. Why not all of the above? Even the contradicting ones~
Here might be an interesting idea, when he over uses his ability (in scale, power, or on someone multiple times) have those who are affected lose all memories of the mc. This could make for a tragic saving scene. His lover or family member is dead and he activates his power to save them, they wake up and ask who he is and he has to live with the fact that he is essentially dead to that person. Or for some of his power to activate he has to give up that amount of time in his life span or happiness. He rewinds a large battle and all of the time it took starts to build up and eventually he has to spend X amount of time in hell. Like fate or the heavens are mad for his tampering and make his life miserable for each second he rewinds.
You could do it like Legend of The Sun Knight. Spoiler: LSK Ability Reprocussion When he revives anyone he loses a part of himself because of the immense power required for the spell. For instance after reviving on of his friends he lost his sight. When he uses his power to reverse small events there can be no side effect. But as he reverses bigger and bigger things/events then it can take it's toll on him be it self injury whenever he has to use lots of power. If he reverses anyone's death he could lose a part of himself as compensation or the dead person returns having lost a part of themselves. (Not necessarily a body part. They could just return as a slightly different person.) You are giving him one he'll of an OP power which is cool and all but to make it into a good balance he should have an equally severe Reprocussion to use of these OP powers.
How about having diferent kinds of backlash depending on what he remove/redo? Small things, like a rock throwned at him just making him unable to use the abillity for 1 or 2 sec and in case of something major, killing thousands or bringing someone from the dead, give him severe body damage or something that puts him in a seriously bad situation.
Tatsuya has to experience the physical pain in order to heal but doesn't gain memories. What I mean is the complete opposite, he gains the memories of the death or injury as if it were his own but doesn't experience the physical pain.