... Bards in DnD sing songs, the chinese scholars (a xianxia class, apparently) recite and write poems and draw epic paintings while merchants make deals, magical or otherwise.
To me, a creative way of magic might just be walking and breathing. In most works, breath techniques are used alot because it is an instinctive act that you can build up upon. Soul of Negary has Iron Breath which greatly increases bodily defense and hamon sun breathing that allows the user to shoot out sun rays and not do sick katana spins.
There is also walking, sleeping, sitting stances in Taoism, where going by a routine can improve one's constitution. So how about we go there, a promise to do mundane things for magic?
Walk 100,000 steps a day to gain buff in legs, further buffing can occur but the streak mustn't be broken otherwise the buff is weakened or even lost. Stare into a light source to gain the ability to absorb said light and release at will, more light absorbed equal to more energy stored and can be released as eye beams. This can be a simple logic in the world, where everyone just makes a small promise to do a menial task daily and gain respective quirks. If you want, you can have MC have something simple, like whistling until he can make an ear piercing noise. Also, to copy the power copying in most recent works, everyone in this world can do whatever the other person is doing to maybe gain their quirks, the issue is the amount necessary to clear the bar is different for all. MC can learn the promises of others in order to improve on himself but he must weigh his own promise to others'