There could be a kind of 'style' you can unlock/learn from Genya.
Where you can slice off part of a demon and eat it, gaining some of their power, also unlocking you some demon abilities temporarily.
Unlocking this ability could limit or remove your ability to gain a breathing style.
In the sunlight, when you would normally die as a demon, as a slayer who has eaten a demon your demon power would vanish away slowly until you reach the minimum amount, and at that point your demon form automatically deactivates.
The same things that give sunlight immunity for demons, works for users of this ability also.
Your starting demon power when you activate your demon powers is a specific amount, at first at the low levels of this ability, like when you first get the ability, you don't have any starting power, but as you progress this ability your starting demonic power is higher and higher.
Once you upgrade this power some, even in the daylight when you don't have your powers active, you show signs of the power, such as increased regeneration, increased strength, speed, things like that.
As you eat more demon flesh you get more demonic power and you start to look more and more demonic, starting from the eyes, and then the teeth.
Also, you could gain attributes relating around the demon you ate, from eating their flesh, like how after eating Kokushibou's flesh Genya gained his Eyes, Hair, Demon Slayer Mark, and even his shotgun/weapon gained the appearance of Kokushibou's katana.
There could also by a system to store demon flesh for later and eat it mid-battle.
This could be achieved using some kind of Capsule, that you would buy, maybe from Tamayo.
When you equip these capsules and cut off some demon flesh, it would be stored for later, allowing you to eat some demon flesh in any area and in any condition.
Also, as you grow stronger and eat more demon flesh, you can cut off flesh from higher and higher level demons, and store it.
You could chose to activate and deactivate your demon powers at will, like how in the fight against Hantengu, Genya could activate his demon powers without eating any demon flesh.
When activating your demon powers, depending on your progress with the ability (how much demon flesh you have eaten, or something, maybe the stronger demon you get the flesh from the more XP you get from it towards your ability) and the stronger you are the more demonic power you can get from consuming demon flesh, sorta like a bar, like the equivalent of the breathing bar.
I'm sure this is plenty of info and potential applications/ideas, and I hope you take this into consideration.

dracathereformed You’ve Reached Level 6