A human reincarnated or summoned into a medieval fantasy, galactic fantasy, western fantasy, eastern fantasy, modern fantasy with the power to summon other versions of himself in the multiverse and when he summoned them he gains a bit of their power or intelligience.
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My idea is really simple
All versions of that human in the multiverse and other dimensions became a protector like you know guarding their verse. Like they became a wall an indestructible one since there are many versions of them in the multiverse that they all gathered together and became a massive wall and when they merge together they can become a massive and indestructible wall that can never be penetrated.