にせよ
also: せよ
Meanings
1
even if; even though; granted that
Concessive expression meaning 'even if it is the case that...' or 'granted that...'. Used to acknowledge a condition while still asserting the main point. Often follows nouns, na-adjectives, or the plain form of verbs/adjectives.
Even if you are a child, you must not do such a thing.
Whatever the reason may be, being late is being late.