Sachaewangui Cheonjaesonja

Mu-Hyeok Kim, grandson of the legendary "Loan Shark King," has done all of the family's dirty work for 30 years, only to be betrayed and killed by his uncle's orders. Mysteriously, he wakes up in 1990, in his first year of high school, just in time to save his grandmother on his father's side from a heart attack. Now in need of money to pay for her hospital bills, Mu-Hyeok goes to his mother's family to ingratiate himself with the Loan Shark King, but this time, he plans to take his money and get revenge.

(Source: WEBTOON)