Hyper analyzation of what Zera might like about Jaibo (in my opinion).
These are mainly headcanons to be honest... (LONG)
Zera seems to appreciate the feminine parts of Jaibo mainly (not surprising), such as:
• Jaibo's hair - in some official arts, he can be seen resting his hand on top of Jaibo's head or at least he's touching Jaibo's hair in a way or another. Even in Usamaru's initial sketches (?), Zera's palm is neatly placed over Jaibo's hair. Maybe Zera likes petting Jaibo, who knows.
• Jaibo's physique - while I believe Jaibo's body isn't entirely girlish, there are some parts of it that do resemble femininity more than masculinity. Again, in slightly more recent official deawings, Zera is holding Jaibo by his waist, I find that cute. Does he do that so he can always pull him closer?
•Jaibo's lips - I wished they kissed more in the manga, their small kiss that they shared on the throne is my everything. Zera seems like the type to give small kisses, just to feel what needs to be felt then move on. This also brings me to Jaibo's slightly "primal" way of kissing, he seems to always try to deepen kisses, I wonder if Zera likes that.
Excluding the feminity, what else could catch Zera's eye?
•Jaibo's hands - I like to think he takes his gloves off when it comes to holding Jaibo's hand. Considering that he often has them on, his hands must be warm. Jaibo's hands are probably cold... if I assume he always carries metallic stuff with him.
•Jaibo's way of speaking - Have you noticed that they speak in very different ways yet complement their speeches? Jaibo tends to talk in third person, I've noticed...("I wanna taste Zera too!"). He has a pretty childish way of speaking (well he is 13-14 after all). As for Zera, he as a mature tint to his words, often using complicated terms that a teenage boy wouldn't really know. Yet he does talk with Jaibo...
•Jaibo's personality/behaviour - not so girlish here, at least not stereotypically so. Jaibo is gross and he doesn't hide that, he acts like an insane animal. He was drenched (meh, maybe just splashed slightly) in blood at some point and Zera was still viewing him as beautiful. I think Zera has this capacity to view Jaibo's beauty through his gruesome behaviour, I really do think that.
To conclude, I think Zera likes Jaibo a lot, and that might be because I'm insane 👍🏻