. . . although I have to say, I really don't think I like her character much. Sure, she seems compassionate, but I was really bothered by how she kept the truth about Tartarus and the Dark Hour a secret, especially towards Yukari. She had to have known the latter's motivations - to learn the truth about her father - and yet she deliberately kept her in the dark out of guilt for her grandfather's mistakes. To me, that seems cowardly, hypocritical and downright manipulative.
Maybe I'm wrong, since I haven't finished the game. And I still think you did a great job!
Guilt is understandable, so long as other aren't harmed as a result of it.
But, I've done some homework on the matter, and I believe that I've severely misjudged Mitsuru. It seems apparent that she never knew who Yukari's father was; she seemed just as surprised as anyone when it was revealed to them. This theory makes sense to me, since there were things about her family's work that even she didn't know, and Yukari kept her motivations largely to herself. Looking at it now, I think she would have been up front with her from the beginning. The other S.E.E.S. members would have joined regardless - especially Junpei and Fuuka - and I think she knew that.
As for the rest of her character, there was a lot about her that I actually really admired: strict and responsible, but not overbearing; intelligent and wealthy, but not stuck up or frivolous about it. She's about the closest thing to an admirable rich girl you can get.