Ninjar.io is a good Diep style game in which you can use various Japanese weapons and check out your fighting ability for free. Play as a ninja and your mission is to become the top player. You need to survive and reach the highest level. After you spawn, do not forget to collect as many sushi as possible. Consume food and you will gain stamina along with XP. You can obtain much more experience and unlock the next stage quickly. When you progress like that, you can spend points to buy upgrades for your stats. Besides, you should not ignore new gear appearing on the right-hand sides. You are able to choose one of them to add to your inventory. Aside from attacking the real characters, you can eliminate NPCs. Not only that, you are advised to jump over obstacles on the path or dash to run away from stronger enemies. Good luck!