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I have a really dumb idea... So imagine that the marleyans in aot are experimenting on the titan serum right? And a spider, you heard me, SPIDER, is injected with the serum. But nothing happens so they give it to one of the shifters for some dumbass reason, and they decide to take it with them to paradise.. but when they break the walls the spider escapes and bites the main character. Not Erin.. a male reader. And he uses the spiderman powers with the fucking odm gear....
I made most of that shit up on the spot, but imagine a scout with the BASIC spiderman abilities, maybe venom shock, because the way titan shifters are hit by lightning... I don't know how the spider would come to exist, but still, basic gist is they experiment on the spider with the titan serum, spider gets out and bites some kid when the walls fall. And now, a scout with spider sense and wall crawling.
Maybe Erin's dad can be the one experimenting and the reader is Erin's sibling? Idk. Still that sounds dope. Hell you could if you wanted find a way to give him web shooters... Like he is adopted by Hange and with her help makes them, or if the webs are organic like in the first spiderman trilogies.. but you don't even need to make web shooters as they wouldn't really do much for the plot.
Hell we could be Erin's sibling that isn't obsessed with joining the scouts persay, but are geniuses, spidy ritual, that is fascinated by the odm gear. Who ends up joining the scouts to be by his brothers side.
That'd be a dope ass story to read, just saying.