Re: (Nutaku) Milenium War Aigis (English Version)
I'm just not sure what situation rogues fit into...at least at the point in the game I'm at right now. She costs 11 to drop. I could do a valkyrie for 13, and she's WAY better. I could almost drop 2 soldiers for 11. Granted, I've only leveled Berna to about 20, but she doesn't seem to be anything special. A heavy enemy can nearly kill her in one hit.
Thieves generally have the assassinate skill. It's a chance to one shot the opponent, and can even drop armors in one hit. They also have a high evade chance, so they can ignore all the damage regardless of magical or physical. However if the evade chance fails, they gonna take the brunt of it, as their HP is weak, and they are lacking on defense and Magic Resistance (MR).
Loosely translated from the JP wiki: "Thieves can make or break some of the hardest battles in the game. Their ability relies almost entirely on luck, but it can pull you out of a bind on some maps. It shouldn't be overly relied on though".
For me, I'm not a fan of em either. However, there are a few maps that having a thief can be a great boon, as they are typically one of the cheapest units you'll run into. In a speed drop map (dropping units asap) a thief can be a good choice as they can hold their own for a short while as long as they aren't dropped directly in front of armors.
When I beat "Castle Retake" (and happy with that 1 star!), I did it cause of my 5 cost thief. With out it, I got over run every time with in the first 60 seconds of the game.
It's something to think about. I'd say it's wise to keep at least one around and hopefully you can get another of the same so as to combine and reduce its cost.