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もらわねば

must have (someone) do, must get (someone) to do

→ 貰う
もらわ receive, get + ねば necessitative (must)
auxiliary Rare #44,901
must have (someone) do, must get (someone) to do A formal or old-fashioned form of もらわなければ, commonly used in the expression てもらわねばならない to mean that someone must do something for you.
JA: 医者に診てもらわねばならない。
EN: I must have a doctor examine me.
Conjugation of 貰う
Necessitative
もらわねば

君に行ってもらわねば承知しない。

You must go, or I won’t accept it.

やはりあの人に来てもらわねば…!?

I knew it—we’ll have to get them to come after all...!?

— 崖の上のポニョ (2008)

あなたはすぐ医者に診てもらわねばならない。

You need to see a doctor right away.