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Ifrit was practicing his abilities on his house when he suddenly had received a mental notification through floating runes.
In Hell, a dimension different from this Universe, demons were allowed to leave only when they were chosen by other inhabitants of the dimensions, through summoning magic.
When Chaos was about to summon him, Ifrit received this notification.
Of course, demons are not forced into this, as it would be like kidnapping, and Lucifer, the king of Hell, wouldn't allow his demons to get kidnaped so easily.
The demons had the choice of rejecting it.
But it was often seen as an opportunity by many.
Their society encourages them to accept this offer so they can grow stronger through traveling to faraway places, protecting their masters from dangers, and growing stronger with them.
Of course, there was also the risk of dying…
Check "The Protagnist's Sister Is Actually the Strongest"!