I'll be (not) controversial and tell you straight up... forget about Index. Maybe watch season 1 if you really care. Railgun, Accellerator and whatever other spin-offs exist and will come out... they are all better than Index. And mostly self-contained.
Even if there was no yuri romance I still think it was an amazing story once the parents died, the Marnie had no family except for an infant Anna who didn't have time to meet growing up because Marnie died soon after that. Marnie desperately wanted to meet Anna when she was older and wanted a friend because her life was so sheltered in that mansion.
^^thinking about them as grandma and grandchild still makes this image feel warm, though familialy, for me. Reminds me when my grandma used to hug me—now I'm way too big hahahaha
^yeah railgun is more fun than index and i really hate touma he is not a good protagonist and i have to say my ship is mikasa x shokuhou i think they are cute toghether
So far I've only seen the 1st seasons of Railgun & Index so I'm not sure what happens afterwards.
Funnily enough I did like Touma's character before they pulled the amnesia bullshit. He was snarky back then and just instantly became a boring push over.