就是…也【jiùshì … yě】

就是 opens a "what if" and 也 in the next clause says the outcome won't change. It's spoken; the written equivalent is 即使…也.

With 再, it covers any degree: "however".

就是 + a noun

Before a single noun, 就是…也 means "even X", for an extreme case. 连…也 does the same.

就是 also means "it's just that" or "exactly". A 也 later in the sentence marks the "even if" reading.

也 is not optional

Without 也 the second clause has nothing to hang on, and 也 goes after the subject, before the verb.

• × 就是下雨，我去 → 就是下雨，我也去
• × 就是下雨，也我去 → 就是下雨，我也去

就算…也 and 哪怕…也 mean much the same. 就算 is the most casual, and 哪怕 pushes towards an extreme.