なり始めた

started to become

→ 成る
なり become; come to be + 始め start, begin + Past tense
verb · past indicative Rare #40,396
started to become
JA: 空が暗くなり始めた。
EN: The sky started to become dark.
Conjugation of 成る

ここは寒くなり始めた

It’s starting to get cold here.

その問題は国際的な性格ものとなり始めた

The problem has begun to take on an international character.

彼女の親切私には重荷なり始めた

Her kindness was beginning to feel like a burden to me.

彼は怖くなり始めた

He began to get scared.