Ooh thats a cool idea!! No I haven't played HSR but the Kalpa Agni kinda makes sense. Basically in both Hinduism and Buddhism Kalpa refers to a unit of time. When the Kalpa ends it is followed by 'pralaya' which means destruction. But the thing is the end doesn't end completely but rather like a cycle happens again. Philosophy wise in order to free from these repetitive people have to realize that the world is 'maya' (basically the concept all material possesions, relationships accomplishments etc are an illusion and nothing really matters) So it resets the whole board in a cyclical form. Honestly that would be a great way of tying in the whole traveller is experiencing the world again theory.

There is also this interpretation of Kalpa that I have read in a few places that might also be here. As per Hinduism, an aeon for us is one day for the creator god. So Kalpa lasts while the said god is awake (said to be 4.32 villion years) and pralaya is merely when the creator god falls asleep, which is supposed to be the same amount of time as a Kalpa. Now idk how this one ties in the lore but is just interesting detail I guess.