I remember the first chapter cleary but forgot the name

The MC was a 14-15 years old boy who seek a romance aka love and in desperate on having a girlfriend.

he always confess his love towards every single beautiful school girl he encountered (seems same age as him) , and got rejected hard.

after his last rejection, he stumbled with his 3-4 friends , that laugh at him. One guy seems was one of his good friend, that told him like "geez, stop that kind approach of confessing, cut it out dude you need to do more productive to do", while the other just tease and laugh at his effort.

he ignore them anwyay ,and when he was buying something at convinience store, he got a love struck with the cashier woman(adult woman).

he then falls in love and because she was an adult, he try to impress her. He always clean the front store and always buying something there so he can always meet with her.

One day when the boy picking a trash in front of the store, there's some middle aged man that got harrased by thugs. The boy then somehow help that man(i think he want to impress the woman). People who watches it then clap their hand and say "hey that was the person who always picking up trash in our area, he's a good boy and even he help that man"

after that, the cashier woman go outside and surpised at the event. She then say thank you to the boy for helping his husband....

after found out she already married, the boy got into depression, he walks away like zombie and suddenly got hit by a scary looking girl that was riding bycle ? or maybe motor cycle. The boy falls in love with her and follow her.

Somehow suddenly happened(i forgot) like some accident and the boy was knocked out.

The boy then woke up and a professor was smiling on him and make an experiment on his body.

turning the boy into a super human and he forced to wear a super hero costume ? and fighting against monsters.

edit : it's not rat man

the professor was an old man