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なるそう

will apparently become, is said to become

→ 成る
verb Rare #40,702
will apparently become, is said to become そう here reports information the speaker has heard.
JA: 来月から先生になるそうです。
EN: Apparently, they’ll become a teacher starting next month.
Conjugation of 成る
Quotative
なるそう

天気予報によれば今夜は雪になるそうだ。

According to the weather forecast, it’s expected to snow tonight.

ラジオによると、明日は雨になるそうです。

According to the radio, it’s going to rain tomorrow.

休校になるそうよ

I hear the school is going to be closed.

— 嵐の中で (2018)