expression, suru verb (irregular)
return a favor; repay kindness
Used when someone does something good in return for a past kindness or help received. Often implies a sense of gratitude and obligation.
いつか必ず恩返しをします。
I will definitely return the favor someday.
彼は育ててくれた両親に恩返しをするために
He worked hard to repay his parents for raising him.