Rather ask yourself how did they have their normal clothes at approx. 2000 °C for 4 billion years. Oh and Mokou constantly regrowing her sleeves.
Hourai power restores it. Look at the bonus page from the first part of the doujin(it's not on danbooru, iirc).
The hot daytime is 32 hours long...And the lengthy night spans 50 hours.Vegetation-like lifeforms exist, but no sentient beings.Except for two persons...