この規則はどんなときにでも当てはまる。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

rules; regulations; conventions

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

what; what kind of; (with -temo, demo, etc.) any(body, thing, means, etc.)

by the way; incidentally; sometimes; occasionally

but; however; though; nevertheless; still; yet; even so; even; however; no matter how; even if; even though; ... or something; either ... or ...; neither ... nor ...; pseudo-; quack; in-name-only; for lack of anything better to do

to apply (a rule); to be applicable; to come under (a category); to fulfill