ねばならない

ねばならない expresses a strong obligation or duty that something must be done. It is somewhat literary or formal and is more common in written language or formal speech; in everyday conversation, なくてはいけない or なくちゃいけない are more natural. The form attaches to the negative form of a verb (the 未然形 combined with ねば) to mean 'must do X.' It emphasizes necessity or an unavoidable requirement, often due to rules, duties, or consequences.