All summoners can personally use the power of their primary summon without needing to actually summon the beast on the field. This is basic knowledge.
This gives a summoner a decent amount of defensive capability.
Typically, the primary summon for most summoners is the first beast they have ever summoned in their lifetime.
Some summoners also change their primary summon if the original one somehow ends up breaking the contract and ends up going back to the spirit realm.
Although it's rare, it happens sometimes.
But even in these scenarios, a summoner can still only use the power of one beast without the need for summoning.
Summoners are weak as individuals; their strength lies in group fights.
Thus, to make up for their total defenselessness, they use the power of their primary summons when the need arises.
They generally use this power to stall some time so that they can summon their beasts in the meantime.
