My made up continuation:
The humans of that world summoned the other boy to defeat the beast people.
The other boy got powers and united forces with humans so he could maybe save our mc that tried to save him.
Already on war both sides clashing, somehow powered boy met with our mc, they talked and powered boy stopped the war, they made an alliance, powered boy became king, everyone is happy (outside of the original monarchy and possibly church summoners who were defeated)
Also god is very powerful so he intervened in the summoning putting their hand selecting the summoned boy so would be a good one and letting mc also arrive so all this plan would be successful
Yes yes thats nice but what about the war?? Or the other guy that got summoned why add those foreshadowing plot if its a one shot