I know you asked for crit, but I honestly don't have anything to offer, characterization-wise. Your characters are amazing, as always, and you're able to handle such varying degrees of personalities so effortlessly. It's very commendable and you should be proud.
I love the way you're playing Ueda so far. His intro was wonderful. Cute and creative without having to be over-the-top, and did a great job show-casing his personality (I can say the same about Fay's entry, too). He's the only intro recently but even from this small example you can see that you've taken to heart the crit about generic intros you've received in the past. I love seeing him interact around, as well.
I continue to be in love with Ioryogi as well. He's so much fun and so silly, but I love his more serious entries/threads lately. I think he's very versatile and you're doing a great job with him. Your other characters, too. I love seeing Sakura around more and her thread with Kuro, I loved the way you handled the recent even with Syaoran, and I think that you did a good job with Fay in regards to Fay-sensei's return. It was emo without being cloyingly so.
I think your activity has been improving, as well. I know it's something you've been really working on, and it's great to see all your characters tagging back more consistently and building new CR while maintaining the old. I've really enjoyed stalking your threads and look forward to more in the future.
I know you are also thinking of picking Sei back up, and for that, you wanted opinions. Rather than saying yes or no to that, I'd rather just ask you to think about the reasons why you dropped Sei in the first place, and almost dropped him once before that before changing your mind. Think about the reasons you dropped him. Are those issues/reasons still there? Try to think past the temptation of this event in particular. Do you think those reasons for dropping before have been overcome? Or, if they aren't overcome, are they worth putting up with this time around? What about this time makes it different?
I'm not asking these questions to be condescending or dismissive. I think it's the best thing to ask yourself when considering picking up someone you've dropped before in the past. Can you see yourself playing Sei for the long-haul, or will it be a case of temptation that will dwindle away until you're hardly playing him again? He's hard to socialize with, for sure, but before you dropped him he was barely passing AC, and only did so with the help or either Subaru and Hokuto. Obviously he won't have tons of CR or sparkly best friends, but is that half-stasis something you can overcome or put up with?
Admittedly, part of me is afraid of your character count being too large. Remember that very recently you cut back on a lot of characters in order to improve your activity. Since then, you've added new people. And while your activity now is very good, I'm afraid of you creeping back up to the level you were at before and having to rinse and repeat the same dropping of characters as before. I do think that, personally, you do have a good level now and you should work to maintain that level of activity. Especially since right now there is the bias of new muses (Ueda and Fay, and Real, too, having just recently gotten a perm account). That isn't to say I don't love Sei and how you played him, but it's still a concern I do have.