(Oh this should be a very fun stress test of memory)
You were standing in a vast field of grass, mountains towering in the distance, the sky was dark and stary with nebulas of various vibrant colors. A moon could be seen in the sky, big and ringed, this wasn't earth. Ahead of you stood your rival, that hero that did all she could to try and beat you, the supposed strongest of all infinite realities, while she does heavily surpass you by light years, for some reason you just had something specific that countered her.
Ultimate Reika, floating in the sky with a red hue of energy around her narrowed her red eyes, she didn't look happy. She clenched her fists, willing to go all out to beat you "You wanted a fight? I'll give you a war!" She raised her hands into the air "I BRING EVERY EXISTENCE TO ME!!"
Portals snapped open, red glowing rims with a void internal, one by one lining ahead in the vast field, some bigger than others.
"I already informed them all with my power... You will fall" Reika announced, her voice echoing, blonde hair whipping from the wind
The first set of portals out walked a large group, in the lead a tall professional guy, Sensei, behind him a bunch of students with halo's. And Tendou Aris to the side with a giant railgun "Blue Archive reality! show them Cute and Funny can fit in, let your anger on normies fuel you in battle!" Reika called out
The next portals opened in the sky, a massive purple starship with energy shields flaring already, looming over the entire battlefield with its city sized length belonging to the Covenant, human designed ships of the UNSC following soon after "Halo reality, glass them and do not let them out of your reach"
2 portals looming 300 meters in the sky slammed open shaking the ground, a massive Kaiju's growl echoing as it emerged, massive gody, dorsal plates glowing blue, Godzilla Earth. The other portal a Kaiju with similar height stride out with thunderous steps, more thin and more arms, its eyes glowing purple, King Titan "Uhh... crush them? Godzilla and Ark teaming up? odd... either way, keep your undying contract going!" The King Titan gave a single glance to Godzilla Earth, the look when two alphas challenge before looking back to you
Further ahead of the Kaiju's in the back opened a few 100 meter tall portals, 2 humanoid mechas jumping out at high speeds, purple and green, red and orange "Evangelion reality, 01, 02... Impact him"
Ultimate Reika gained a smirk and looked back at her still growing army "One Punch Man... let your arrival be known!" She called out. Suddenly a bald guy looking bored appeared in front of the Eva's, Saitama "Can I go home?" He asked in a bored simple tone
"...Hehe... A certain reality I am quite fond of" Ultimate Reika began, a new set of portals small, 2 people walked out followed by some more in the back a chestnut haired girl and a slightly taller boy with white hair "Toaru's reality... Work together as level 5's" Accelerator gained a sharp thin grin as he stepped forward once, clearly excited to go, his voice raised in glee "I may have gotten weaker, but I am still as strong as they come" Mikoto Misaka next to him scoffed at him, cyan electricity igniting around her
More portals opened, some will even open when your not aware during the fight, the army growing in size, Kaiju's, Mechas, Heroes, Espers, Starships, Gods, Villains and corrupters. All of them against you, all in a single team. The biggest in the back, Godzilla Earth's slow thunderous steps far in the distance a big threat, he can always see you. There were more Kaiju's out there, one tall with a massive tail and too many sharp teeth, dorsal plates radiating purple, it looked like it was suffering just being here, just smaller than them
Ultimate Reika lowered remained in the air, red eyes narrowing "What hope do you have? ATTACK!!" With you a mile out, the closest to you being the MHA, Blue Archive and Toaru realities, good luck.