であれ / であろうと

1. 1With a question word, "no matter who/what/where X is," meaning the outcome does not change whatever X turns out to be.Ex. 1
2. 2With どんな + noun, "however X it may be," stressing that even an extreme case does not change the result.Ex. 2
3. 3With a specific noun, "even if it is X" or "granted that it is X," meaning that X is no exception to what follows.Ex. 3

A formal, written-style pattern used in rules, statements of principle, and firm declarations of resolve. The main clause often states an obligation, a general truth, or an unchanging intention, but it can also report what actually happened regardless of X. であろうと is the volitional-form variant with essentially the same meaning, and both are stiffer than everyday alternatives such as でも.

• 1.
  であれ〜であれN2「であれ〜であれ」 pairs two nouns or な-adjectives, with 「であれ」 required after both, to mean 'whether A or B'; 「であれ / であろうと」 itself states only one item, or uses a question word to cover all cases. Both lean toward written style, but their sentence structures differ, so they cannot be directly substituted for each other.
• 2.
  にしろ / にせよN2「にしろ／にせよ」 also expresses concession; when attached to nouns it can mostly be interchanged with 「であれ / であろうと」, but its tone is less formal, and 「にしろ」 is also common in speech. It can also attach directly to verbs and い-adjectives, and can pair two items as 「AにしろBにしろ」.
• 3.
  といえどもN1「といえども」 can be interchanged with 「であれ / であろうと」 when it attaches to a concrete noun to mean 'even if X'; both are written style. It can also attach to verbs, the plain forms of い-adjectives, and minimal quantity words such as 「一円」, and the second clause is generally not a plain objective statement.
• 4.
  にしたってN1「にしたって」 also means 'even / no matter... still,' but it is colloquial, attaches to verbs and adjectives, and can also mean 'even someone like that,' often with a nuance of dissatisfaction; 「であれ」 is formal written style and does not attach to verbs. When the meanings are close the two can be swapped, but their registers differ.
• 5.
  ともN2「とも」 mainly attaches to the verb volitional form and to 「かろう」, and works in both verb and adjective sentences; with nouns it appears as 「であろうとも」, which has the same meaning as 「であろうと」 and can be interchanged with it. 「であれ」 attaches only to nouns, question words, and な-adjectives.
• 6.
  とてN1When attached to nouns, 「とて」 is close to 「たとえ〜であれ」, emphasizing that even that object is no exception; it can also attach to verbs and adjectives, and its second clause is often a futile, negative outcome — whereas 「であれ」 cannot attach to verbs. Its tone is more archaic.

Unlike であれ〜であれ, which pairs two alternatives ("whether A or B"), であれ / であろうと takes a single X. にしろ / にせよ and the colloquial にしたって are close in meaning. といえども and とて concede a specific noun ("even X"), and とも follows verb volitional forms and adjective く-forms rather than nouns.