Those actually appear to have a flat bottom given the circular-bottom shape, so those would actually be flat-bottom flasks instead of round-bottom flasks.
End of episode 1 plot twist: the hero joins the Demon King.
How havent we had that yet? The closest we got is _Hataage! Kemonomichi_ where the protagonist straight-up refuses the Princess' request, even physically attacking her before running away to do his own thing.