Saikyou no Onna Reika to Ryou -Koujoku Kuppuku no Kiroku-

The main character is an ordinary school boy.
One day, he was tangled with a group of yakuza in a forest of neon.
He thought he managed to escape, but he was found by one of these men in a park.
He thought it would be end of his life, then Reika, who was during the course of training, came to save him.
Eventually Ryo appeared and they started chatting in a cheerful way.
The main character was in a daze, and when he came back to earth, they were already surrounded by several men.

[From DLsite English]