also: なににでも
adverb
everything; anything; for everything; in anything
Used to express that something applies to all things or any situation. Often appears with verbs like 使える, なる, 合う, etc. The particle に is part of the expression, so it typically follows a noun or nominalized phrase.
See also: 何でも
この道具は何にでも使えます。
This tool can be used for anything.
彼は何にでも興味を持つ。
He takes an interest in everything.
あの人は何にでも文句を言う。
That person complains about everything.
何でも means 'anything' or 'whatever' and is used as a noun or adverb without a specific particle. 何にでも specifically includes the particle に, so it is used when the following verb or adjective requires a に-marked complement (e.g., 使う, なる, 興味を持つ).
Compound of 何 (what) + に (particle) + でも (even, also). The reading なんにでも is a contraction of なににでも, which is common in colloquial Japanese.