Index/Railgun, but this is likely to happen anyway.
Usagi Drop, also likely to happen.
Kokoro Connect, but only if they can track down Balloon Vine's civilization and lay waste to it.
The problem with Shinjeki no Kyojin is that there is never likely to be a sufficient amount of payback. They could seize all the "special" titans, and whoever may have sent them there, torture them for decades and it still wouldn't be enough to make up for what they've done. That was my big beef with the series in general though.