even if; whether ... or ...; though
Concessive expression used to present a hypothetical or extreme condition, often paired with another にしろ or similar phrase for 'whether ... or ...' patterns. Similar to にしても but slightly more formal or written.
Even if it rains, the match will probably be held.
Whether you go or not, please decide quickly.
Formed from the copular continuative に and the imperative しろ of する. The construction became grammaticalized with concessive and alternative meanings such as “even if” and “whether.”