I mean one of the points of criticism I'm certainly going to give Reborn deductions on is the too many characters syndrome. So yes, I clearly think even more characters need to be added. Sarcasm aside, I feel that we should break it down what you're asking for or suggesting removing each obstacle one by one:
The game needed to start tying many things up 2 episodes ago. I love all the arcs and the large cast don't get me wrong, but it feels like we start an arc with half the game as a buffer before it starts tying all up. Definitely hope a lot of arcs start getting answers very quickly but I did like the pacing of the OTS crew and their interactions are some of the best (still think Fern vs Florinia if you defeated Solaris is such a good reflection on what's really going on with Florinia).
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Alright so now that we established that there's way too large of a cast (not Reborn's fault exactly), let's say there was an opportunity to add such a character. What unique aspect would they bring to the plot? Honestly, with the context that we have it'd pretty much bring little or next to nothing. Not a new character, but the fact that they are gender confused or their arc is reflected around it.
I will say this three times. Gender does not define a character. Gender does not define a character. Gender does not define a character. Got it?
What I'm basically saying is that just because they're a certain gender, doesn't mean they have to act a certain way. Cain and Titania are the best examples of breaking their stereotypes. In fact, I bet these two have more conflict with society than a "gender-confused" character just due to the way they are. In fact we explore many different kinds of conflicts but Reborn's center of attention is always back on the league and meteor.
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Okay, now we established many things a gender confused could bring to the table could be instead use to better flesh out both the world and other characters instead of putting time and effort into a new such one. Adrienn probably needs more screen time anyways. But what if we did go the route and have a nb/gender-confused character? How would they fit in to the plot?
Reborn seems very welcoming to all types of people most likely due to the horrible conditions they don't discriminate as much. We actually see a lot of people suffer and/or die simply due to disasters caused by team Meteor. Adrienn fits into this due not to Xe's gender, but by the fact Xe hasn't given up on Reborn and wants to rebuild it back to the way it was. In fact how many characters really even reflect on their gender in Reborn even if they fall into a certain category? Cain? Cain is just playful, but had a hard life at home and left due to his choices in love.
I guess my point is that without context, I have no idea what you even mean. Reborn certainly doesn't need gender-confused characters as the world is not set up to focus on being gender based. I could keep peeling layers and still find no need for it because without context, an idea is practically worthless.