"If we go through life protecting ourselves from hardship, nobody gets stronger."
Mimi does not seem to change a great deal throughout the course of the show. She is also the character to receive the least development (except perhaps the little kids).
Tai has to learn to be a good leader, to overcome his fears and to look out for the others. Sora has to overcome her low self-esteem and doubts about her own worth and ability to succeed and contribute to the group. Matt has to deal with feeling useless and seeing TK standing on his own feet, leaving him uncertain about whether anyone likes him - and whether he deserves to be liked.
Joe has to conquer his own fears, build his confidence, and learn to stand up for himself. TK has to try to keep up with the big kids and wants to be able to look after himself, to be trusted. Izzy has to come to terms with being adopted and worrying that his parents mightn't really love him or trust him. Kari tries to overcome the guilt she feels from the destruction of their city by unselfishly giving everything to be a digidestined.
Unlike most of the others, Mimi does not suffer from a low self-esteem, guilt, or feelings of doubt over anything much, and she never seems to doubt that she is a useful member of the team. (Ironically, she probably is the least useful member of the team. ^^;;) While she is sometimes sad, she is rarely depressed - the only time she was was because of her kind-heartedness - being depressed for the sake of others, not because of some darkness within herself.
Despite her complaints in the digital world, Mimi is a relatively simple and cheerful person who has led a happy life. She is not difficult to understand (well, occasionally she says some pretty ditzy things that makes one wonder if she is of this planet at all) - she openly expresses exactly what she is feeling and doesn't hide any emotion at all.
This can sometimes make the others annoyed with her but it also explains why Mimi doesn't undergo any deep delve-into-her-own-soul-to-analyse-her-own-worth experiences - she has no skeletons in the closet to confront. She "lives her life on the outside", to borrow a saying from a John Marsden book. (Cool writer, btw. *plug plug*)
Mimi does not seem a very serious person - but that is a matter of comparitivity. All of the other kids, apart from sometimes Tai and TK, are fairly serious and logical-minded, sometimes melancholy, and generally good at keeping their cool. (We can exclude Matt from that last one. ^^;) Mimi, on the other hand, is usually dizzy and bright, saying strange things, exhibiting little curiousity, and generally not analysing things very much. She has a "who cares?" sort of attitude to anything outside their immediate concerns and problems.
I suppose what I'm really getting at, in my usual roundabout way, is that Mimi is the sort of person who responds to things from the heart, and bases her way of living on emotions. She's a "Feeling" on the Myer-Briggs personality test, whereas most of the others are "Thinking", although they undoubtedly do respond according to emotion often.
Mimi is not analytical or calculating. She's an innocent, and that means she doesn't see the need to hide things. On the other hand, she also doesn't care to give names to her feelings or to agonise over them - she is more spontaneous and thoughtless than that.
When Joe wanted to strike off on his own, he commented that "Mimi knew where she fit in... but he didn't". Mimi seemed surprised at the idea of anyone not feeling as though they knew their place - for her it was natural, not something she had really thought about.
It is for these reasons I have just mentioned, that Mimi does not go off on any 'journey of self discovery'. It would be out of character - she knows herself quite well without worrying about it. Sometimes she may look into her self and see what's there, who she really is - but that she does with sincerity, not confusing things, just seeing them honestly and simply.
This is why I say she grows up - because she has the child's way of seeing things to begin with (and I think that way of seeing things *has* developed by the end of the series), while most of the others have a more grown-up perspective all along - indicating, I believe, that the others had done most of their 'growing up' before entering the digital world.
To elaborate on this a little more... what I mean is, Joe and Matt, for example, undoubtedly change in the digital world. Joe, in fact, changes more than anyone. They both mature and learn to better appreciate themselves and their friends. But I think that theirs is not quite the same as the way in which Mimi grows up - they are more conscious of their selves, if you like.
Tai becomes more serious and learns things. Matt learns to like himself and to see himself from an unsullied perspective. Joe becomes less fearful and proves himself. (I think one scene that clearly shows how far he has naturally come, is where he offers to take over guard duty from Ogremon - he stands arguing with this monster, perfectly natural and unafraid - where he would have once been terrified, and never able to see himself doing such a thing.)
Izzy talks to his parents, and generally learns value in friendship. Sora finds that her mother loves her and that she can help make a difference. All these characters come away with things they didn't originally have, really. Tai, maturity. Matt, a better perspective. Joe, courage. Sora, better self-esteem. Izzy, recognition of what's important.
Kari and TK do not change very much. TK does pull away from Matt a little toward the end, but that may in part be due to having an equal - Kari - to impress. ^_^. While the two are strong beyond their years, I do not think they come away with much that they did not have in the beginning.
Mimi, however, comes away with a number of changes. She is less selfish, more kind, better able to understand and appreciate her teammates (who were originally "weird kids" in her slightly snobbish opinion), more able to recognise what is important. She recognises courage in herself - as the least boyish member of the cast, courage was not something she really placed much importance on... but she comes to know true strength.
Mimi does have a few things to overcome, as do the others - she has to accomodate herself to living in the digital world, and she has to fight herself to become less selfish. However, the mini-storyline of Mimi's character development is not given a prominent role - it is something we may notice but which is never really shown. There was one time, when Mimi, stressed out, snapped at Tai, and then apologised, saying that "she was being selfish again" - indicating that she was trying to curb that aspect of herself.
Later, she has to find the strength to go on fighting when she doesn't want to. This *is* something she agonises over somewhat, but even then, she does so with sincerity, and does not hide anything.
Mimi advances from her childish weakness to a stronger and more mature perspective generally (albeit still sincere/open and fairly simple).
I will stop writing now because I have completely lost my train of thought and don't even remember what point I was trying to make. ^_^;; Errr... to sum up, Mimi grows up because she had a child's perspective to begin with, and developed that... she doesn't undergo great self-analysis because that would be out of character, Mimi is too open and couldn't be bothered 'discovering' herself because she is so sincere she knows herself perfectly.