Card Collection/Harem (Spoilers)

(Reader x Multiverse Crossover Harem) Your best friend and local mad scientist Mitsuru creates an incredible gun that can shatter the barrier between realities and summon powerful warriors from other times, places and dimensions. It turns out that the world is in danger from deadly alien invaders, and by leveraging a multi-universal love of an anime franchise starring you as the main character, you can summon dozens of women who are madly in love with you to fight back. Sounds simple enough, right?