We can use another generic tank like Ismayel.
The problem with fire emblem is that the only type of magic in it is mage magic. If there was holy magic, you could be a generic paladin (not a fire emblem paladin. I'm talking more along the conventional rpg game paladin, who heals people with holy light and buffs his party).
Fire Emblem really got the idea of paladins wrong. Although they can ride horses and are tanky, that is not what makes a paladin a paladin. They are holy knights who bring religious zeal into the battle, sort of like my second character, except my character won't be healing or buffing the party. So he's not really a paladin.
Anyway, that's completely off topic from what I wanted to say. If you want to go for a stealth guy, I think a serious 100% stealth character who specializes completely on assassinating targets with cloak and dagger play is what we're missing. But do what you want to do most, as long as it isnt a tanky mage guy with an unrelated thief background.
If you had a long warrior background and ended up learning magic through a special event in your life, that would make sense.
Or if you were a talented mage with a mage-academy background, who used frost magic to line his armor with ice for added durability, that would make sense too.
Just realize that in either case, you would probably be a lesser tank than average, and a lesser mage than average too.
Same general concept applies to rogues as well. You don't have to pay attention to this, but notice how physical/magic hybrids are hard to come across. That is probably because it takes a very special event in ones life to lead them to study both fields of combat. So your background would pretty much make or break the character. This is why I love paladins (the non-fire emblem ones), because they are the one exception to this. They are just priests who worked out a lot.
Anyway, I'm getting off track talking about paladins again. Speaking of which...
Welp. Looks like I have to re-write Ismayel's sheet.