Save A Girl, Reward 3 Billion

It was like someone had placed his little insignificant life on a downhill slope towards Doom!
Just before the day of his exams, he found a little girl about to drown in the river, so he couldn't help but jump in the river to save her.
He saved her successfully but got a fever the next day which caused him to fail his exams. He called his girlfriend for some comfort, but got dissed and dumped by her instead!
But all of it changed the day he met the little girl he had saved again!
She asked him to save her from trouble again and watching her innocent and almost teary eyes he helplessly agreed, but he didn't know that this little kindness was about to change his life forever!
"Ding!"
"Diamond Life Super Supreme System Activated!"
A mechanical voice appeared in his mind.
He suddenly got 3 Billions in rewards to save the beauty!? But what he didn't expect was, that it was just the Prelude! And his life was literally about to turn... just like the name of his System implied...