I like every character. I think all of the characters that you can have live from me1 should get some sort of resolution quest in 3. Ranna i can see getting into something hairy again and being killable again "You don't take second chances very well do you?" the raccni queen will defenitely get something, the green asari from feros, helena, fist all seem like they could have something interlinking. also the detective from noveria...hell i could almost imagine a quest involving helena, fist, AND that detective all in one.
theres so many characters from 2 that either i dont remember the name of yet or that didn't get named that really should get some second coming in 3. alot of the surviving members from loyalty quests as well defenitely feel like they can tell more story. theres alot of guys from UNC missions in 1 that could show up again. I wanna see the Consort, the character from your origin quest (the girl from "i remember me" was so sad i wanna see how shes doing) corporal tombs should show up, there's a couple other dudes that you end up killing throughout those quests that can also survive that should show up. theres just so many. I want to meet EVERYONE.

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it would be interesting if they featured all of the city areas from both games in the interest of meeting more and more characters. (Including the dlc areas from me1, they seem like places you could revisit for story and character interaction)
Also Balak. bring that guy back, need to shoot him.