A very powerful god is currently travelling time and space to fix worlds, universe, timeline, parallel worlds that have singularities and destroy those that have ran away from their destiny and one day when he was finished from his work from destroying a world that have been invaded by monsters that don't have intelligience.
The god then find another one that have singularities and came to that universe to fix one world that have ran away from their supposed destiny, but it didn't expect that one of the forces that is protecting this world from other singularities that is not supposed to be in this world appeared and because the god appeared to correct this world. This force see it as a threath and when it released its power to annihalate the god it didn't expect it to be too powerful and the god also didn't expect to be this singularity to be not so simple so he fought back too.
But all of that backfired both of them as the force that see the god as being threatened lost many powers and the god's power got sealed in the process, thus making this force win in this fight.
Luckily the god escaped through time and space before his power got sealed. But when he escaped a power of space and time suddenly got triggered and a monster came and hit him and because of his powers being sealed he replaced the conciousness of the monster.
In earth a girl was summoning a familiar and this is her 3rd familiar and when she summoned it, it felt so weak but its cute so she felt like its just like her other summons and didn't mind it, because some of her summons starts at the weakest level and some aren't and this one started at the weakest level.
The girl didn't know that this familiar that she summoned is scary as its the god from before that got sealed and when the familiar got stronger it started to awaken its sealed abilities and while the girl is silently wondering while she is recieving skills and abilities randomly.
In this earth people awakened because of a system that appeared that helped them fight against demons that have invaded this world, and one of the awakened is this girl the master of the currently sealed god and she awakened a proffession called summoner and summoners have the power to summon monsters, beasts, demons, angels from different worlds and overtime summoners can obtain the abilities of their familiars they have summoned. But they can only summon monsters slightly stronger or even weaker than them so they have to make their summoned monsters level up.