(Anime Crossover) Fighting Back Against Mary Sues

One day, my little sister was suddenly replaced by a strange creature! To find my sister, I had no choice but to travel between worlds with help from my friends. But every world I reached had a strange creature in it! W-what on earth is going on?? By chance, I defeated the strange creature in the first world. That's when I learned that these strange creatures are actually called Mary Sues. So I gathered my companions and began my quest to take down the Mary Sues and find my sister... No CP. The protagonist has no romance, but there are romantic relationships for the supporting characters. I'm a high school senior. I go five days a week without a phone. Updates are extremely irregular. I have no backlog and am writing as I go, so enter at your own risk.