For reality-rewriting, the general mechanic will be that characters who have abilities such as these (Archer from Fate/Stay Night being another good baseline example) will be able to use their power to influence an area around them and start to craft it in their image within the scope of their abilities. People of strong wills can resist the changes, and it's extremely localized and only active while the character is focusing and putting power into the effect. Permanent reality re-writing abilities will not be available to any Player Character.