Expressing "even if…" with "jiushi"

就是 (jiùshì) is one of the many "even ifs." Like 即使 , 就算 and 哪怕 it is used to introduce a hypothetical statement, which can then disregarded with 也.

Structure

就是 + Hypothetical Statement + 也 + Action

就是这台电脑价格上万，我也会买。Jiùshì zhè tái diànnǎo jiàgé shàng wàn, wǒ yě huì mǎi.Even if this computer's price is over 10,000 yuan, I'm still going to buy it.
就是降温了，我也要穿热裤，时尚嘛! Jiùshì jiàngwēn le, wǒ yě yào chuān rè kù, shíshàng ma!Even if it's starting to get cooler, I'm still going to wear short shorts. It's the fad!
就是他变成一个穷光蛋，我也愿意跟他在一起。Jiùshì tā biàn chéng yīgè qióngguāngdàn, wǒ yě yuànyì gēn tā zài yīqǐ.Even if he were penniless, I would still be willing to be with him.

Note that the clause used after 就是 must be hypothetical, otherwise 虽然 should be used:

现在虽然是高峰期，但我也要出去。Xiànzài suīrán shì gāofēng qī, dàn wǒ yě yào chūqù.Although it's peak busy hours, I still want to go out.
现在就是是高峰期，我也要出去。

In the sentence above, it being rush hour is not a hypothetical statement, so it is incorrect to use 就是.