https://www.dmm.co.jp/dc/doujin/-/detail/=/cid=d_477836/

[Synopsis]

One day, a dark-skinned gal in his class got addicted to playing card games on her smartphone.
The gal asked the otaku (guy) to teach her how to play card games...
Thinking that he would have more friends to play with, he agreed and as a thank you, she took his virginity!

After that, she asked him if he wanted to do something naughty in exchange for a rare card at school!
His sex trading life with the dark-skinned gal begins!

She lets him do all sorts of things, including blowjobs and anal sex and he falls in love with her and confesses his feelings, but she refuses, saying that she won't go out with him if he's not good at sex...

But the otaku doesn't give up and he polishes his sex skills and attacks her again, making the dark-skinned gal cum!
And she accepts him...

Base +22, huntmonster +6, dokedoke +6, ADIN0 +10, darks1te +6

@The Magi
I think you should add that the initial reason she refuses is because she thinks he could find a better girl than someone like her, until he confessed that he loves her

Base +9, ADIN0 +10