I think you do great in not making Ichiru overly cutesy, or force cuteness into threads, as many kid roleplayers often do. In terms of overall personality and interactions, he does feel like an actual well-rounded character with substance to him, and in turn this does make him likeable and fun to play with.
I wonder about his potential development, however. You've said a few times that you simply enjoy playing him as ill, which is fine of course. But for a child who is constantly sick to the point of being unable to do anything, wouldn't it make sense that, being in a magical land where people have all sorts of skills, he'd search for a way to be better?
This is absolutely subjective and I'd like to hear your thoughts on it, but playing a child who was so limited and sick in his own canon, to me it'd make sense to seek a way for him to at least be moderately better off, so he can have a chance to do things he couldn't before.
There was a suggestion that he'd learn to swim, that seems an interesting thing to have him do. I liked seeing him drawing and playing like a child would, as so many of his tags in previous logs involved mostly being sick, or being hurt in some way. While the hurt-comfort aspect of caring for a scared, sick or hurt child can be fun, if there's no intention for him developing anything from those situations (whether it's physical improvement, or emotional, with his attitude towards it changing as he's now mosly sticking to pessimism and acting defeated and resigned) it feels that he'd soon become a one-trick-pony character.