必ずお返しします

I will definitely return it

→ 必ず

phrase Rare #43,136

I will definitely return it A polite expression used for returning a borrowed item or repaying a debt or favor.

JA: 借りた本は必ずお返しします。

EN: I will definitely return the book I borrowed.

I promise I'll return the favor.

— 新感染ファイナル・エクスプレス (2016)

I’ll definitely return it.

— 魔女の宅急便 (1989)

I promise I'll return it.

— ネバーエンディング・ストーリー (1984)

I'll definitely return it next Monday.