Looks very cute! Well done ;)

Branding of the demon is strong, but the game feels a little barren right now.

What's your target audience for this?

Thanks for the comment! What do you mean exactly with barren? And, how do you think I may fix it?

Certainly:

Fighting and growing is a good, prove gameplay loop that works. It is a series of actions player find fun, but only for a time. There generally needs to be something else. I believe the design currently lacks depth. PVP is one thing you seem to be hinting at, and I'm guessing there will be leaderboards, etc.

But what are the longer term goals of this game, beyond just making your demon stronger from a numbers perspective?

There are several ways to go about putting longer term goals, but these need to be coherent with your current design, so I'm not sure I know enough to suggest any additionnal feature, plus I wouldn't want to stray you away from the MVP so early.

My target at this time is young people (16-25), but I'm waiting for people to play it to see what is my public. I'm not expecting to draw attention before the release. But any suggestion will help me .

Current aesthetics would probably hint at a bit younger than that. Also, the look gives me a feeling you may be able to tap into female players if you play your cards right. Mixed gender games that work are somewhat rare, but your brand looks gender-agnostic enough that it could work, especially if there's more focus on customization of demon cosmetics.

From the above, my current suggestion would be to tie customization with avatar growth. Specifically, have the player somehow unlock new customization items, and have them be pieces of equipment that have an effect on gameplay. Generally though, the latter part generally appeals more to the male crowd, so exercise caution.

These are my 2 cents.

hat way, how you take care of your demon will change also his dexterity in fights. But it may drink alcohol or eat brains if its evil enough. It will always do funny things.

Very cool, but careful about the pitfall here. The downside to a strong brand (as is the case here) is to fall on the "sit and watch" mood, where you just want to see the funny things the demon can do and it is less of a game.

Otherwise looks fun, feels even a bit like Bahamut Lagoon's dragons.