What are some of the hardest champions to make a lore for?

This goes out to the Narrative team, who are known for making the lore and backstories for some of our favorite champions. However there are champions that still retain their pre-retcon lore, and I'm starting to wonder why they're not updating them.

Making lore for these champions may sound easy, but it does take quite an amount of brainstorming to actually think of where they came from, how this'll fit with their kits, gameplay, and personality, and how they'll interact with other champions.

Now my biggest question is, what are some that are super hard to make a lore for? I'm talking about champions that has their own kind of niche that it's nearly impossible to actually create a lore based around that said champion. Champions that were there since the beginning of LoL and now since the retcon, creating new lore has become even harder; especially for champions that were created specifically for the Institute of War. Without a proper setting or story, they can't truly exist and thus can't be proclaimed as a champion.

So what champions that has given you the hardest time to create a lore for?