Tempest of the Heavens and Earth Extra Unlocks

[Tenkko]

So this fangame I was playing for a video has a whole bunch of achievements to get, and getting enough of them seems to unlock some extra stuff to browse. I only got two pieces of concept art, but I was wondering if anyone who played this game enough knows what the rest are (or some alternative way to see them) because... these are some very demanding achievements. Couldn't find anything about them anywhere, either no one ever unlocked them or no one bothered to post them.