"first of all like i said previously, i don't speak english very well but i will try to be as clear as possible. (the game will be fully translated in english of course ,its one of my biggest priority at the moment)"
the basics of the combat system:
To begin with, let's talk about the fighting mechanic in general. You will start the adventure with the basic fighting style, consisting of 8 kicks, 7 punches and 1 special attack that you can use to create a variety of combos. You could also buy weapons to help you in battle. (every weapons has is own special attack).
You could then train at the dojo to get skill points, and skill points can be use to unlock new combat styles or to increase your stats (HP, Strength, speed etc.).
When you start a game for the first time "Kaito Yamazaki" will only have 5 hp, that can be enough for really good players but if you progress a lot in the story you will surely need a lot more to complete the main missions.
You could get your hp back by going to sleep in the evening or by eating consumables that you could get in certain stores, you could also go to a restaurant for example.
Even though the game is a beat 'em up, combat is optional in this game, kaito can earn money by working, selling items to the pawnshop (items can be obtained in some mini games in the aracde room, or by attacking NPCs) if you decide to attack NPCs to earn money or just for fun, then the police will look for you and if you die while you are wanted you will be in custody, you will then have 3 possibilities, pay for your freedom, escape by breaking a wall or wait (this mechanic is inspired by the game beat down fist of vengence).
enemy / friends:
The game tells the story of a group of young delinquent in the middle of a gang war between 2 rival neighborhoods, you could meet rivals npc randomly or by going directly to their neighborhood in which case they will attack you, you would have the possibility to flee or to fight, your allies will be able to come to help you if they cross you. If you die in a fight and you are not researched you would wake up in the hospital.
The story of kaito is up to you, the game only has non linear branch dialogues that will directly influence the story, kaito can grow up to mature and leave his neighborhood to become a good person but kaito can also stay as he is , a delinquent who lives in poverty and who earns his living in an unconventional way. You decide what's next for him.