Okay, I am calculating and I think season 1 will end on Chapter 30. Specifically, this ominous panel.
It will be the perfect hook, perfect intro for the villain for second season, perfect last line for the season as we scratch the surface of the threats looming around the corner for the twins. Plus, since Misasagi has a banger character design, rest assured fangirls will flock to check out him, I mean, the second season just to check out what he does.
30 chapters will be perfect to wrap up in 24 episodes, within the pace we are moving at + the fight scenes will move faster in animation than dialogues. So yeah. Perfect panel to finish 24 episodes without spoiling too much for the next season but introducing all the antagonists altogether in one room.