が必要なんだよ

need [something]

→ が
phrase Rare #27,304
need [something] Used to explain or emphasize that something is needed. The person who needs it is usually understood from context. The particle が marks the thing that is needed.
JA: お金が必要なんだよ。
EN: I need money, you know.

タバコが必要なんだよ。

I need a cigarette.

殺さない理由が必要なんだよ

I need a reason not to kill them.

— ブレット・トレイン (2022)

わたしは妻と子供がほしいので、家が必要なんだよ。

I need a house because I want a wife and kids.

僕の家族には僕が必要で、僕には僕の家族が必要なんだよ。

My family needs me, and I need my family.

お金が必要なんだよ。

I need money.