comfortably; pleasantly; cheerfully
willingly; gladly; readily; with pleasure; with good grace
快く引き受けてくれた。
They cheerfully agreed to take it on.
彼女は快く手伝いを申し出た。
She cheerfully offered to help.
頼みを快く受け入れてもらえると気分がいい。
It feels good when someone willingly agrees to a favor.