Alright, I'm doing it because why not and Yazeed deserves some personality.
These are just my personal headcannons for Yazeed:
He is genderfluid, but since he grew up as a member of the royal family of Matali, he's used to other mers using he/him pronouns.
When they were little, Yazeed and Neela shared a bedroom. This was mostly because they aren't directly in line for the throne and they also were just that close when they were little.
He has adhd. Bright flashes of light can overstimulate him, especially if it's a repetitive blinking.
His parents didn't realize he had adhd until one night Neela had a nightmare that caused her bioluminescence to flash erratically. Yazeed got overstimulated and completely shut down.
After that, the siblings were put in separate bedrooms.
Neela and Yazeed could be fighting like rapid wolves one second and then be laughing and hugging each other the next.
But no matter where their relationship was, Neela would always check to make sure Yazeed was comfortable and not getting overstimulated by his surroundings.
Yazeed would return the favor by helping Neela smile in public because she's self conscious of her bioluminescence.
Yazeed is asexual and aromantic.
Before the plot of the books starts, he was very bubbly and sappy.
He was also the best himbo.
He'd sneak out to parties with Mahdi of course, but sometimes he'd sneak out alone to go to a different kind of party.
More specifically, he'd dress in drag because it makes him happy. He started dressing in drag when Neela started designing clothes because she needed a model and Yazeed fell in love with the clothes, accessories, and make up. He would often use songspells to even change his appearance to appear more feminine.
Once the plot of the books starts, his personality quickly starts to change.
He had a sense of responsibility before, but now he feels the weight even more. Especially when he gets separated from Neela.
Once all the war is over, Yazeed has severe ptsd. It's so bad that there have been multiple times where one of his friends or his family would hurry into his room to him having night terrors. Many times he's sleep-swimming and he's completely trashing his room because he's trying to fight off the terrors.
After the books end, he forms a great friendship with Becca.
Whenever they'd visit each other, Becca would show Yazeed the knick knacks she found and she'd help him create outfits.
He eventually entrusted her with his secret of loving to do drag and she'd support him 100%.
Becca even covered for him so he could go to drag clubs and parties.
A lot of their friends thought they were hiding a secret relationship even though Becca and Marco have a thing.
Marco also knows about Yazeed's secret and so does Elisabetta. Both are very supportive.
Elisabetta even offers Yazeed tips and tricks for drag make up.
When Yazeed eventually tells Neela, she's both relieved and ecstatic. This is because she knew some of her favorite outfits were going missing, she just didn't know who was taking them and she was happy it was her brother. She's also happy because Yazeed trusts her with this secret.
Yazeed has a small home for just himself once he becomes the leader of the Praedatori.
Becca camps out at his home a lot because A) She didn't want to get her own home and B) It's better than sleeping on a makeshift bed underwater or in a tank at the Praedatori headquarters with Marco.
Becca helps Yazeed through night terrors.
She also keeps Neela and the others updated about how he'd doing because he never remembers to do it.
Yazeed has to have light at all times or he starts to panic.
Sometimes Becca will songspell the light so it's blue and it slowly pulses because she knows it reminds him of his sister.(she also knows that if it pulses too fast it'll only stress him out even more.)
His favorite colors are yellow and orange.
Alright, these are just a few of my personal headcannons! Let me know if you'd like to read more!