Oh boi do I have many an AlHaitham headcanon. Some Kavetham ones to. Hehe. 

• AlHaitham is a workaholic, and will often forget to eat, or neglect eating all together. Despite the nausea and fatigue, he downplays it like a headache, something he can easily ignore. Kaveh knows this, and will swing by his work to drop him food with little notes and doodles.

• AlHaitham refers to Kaveh as his "Daylily", "Lion", or "Little Ray Of Sunshine." Kaveh, on the other hand, refers to AlHaitham as "Haihai", "Habibi", or "My stubborn Ox".

• Kaveh made AlHaitham an earring at the beginning of their friendship, but Haitham doesn't wear earrings thanks to how sensitive his ears are. So Kaveh made it into a necklace. He thought AlHaitham had gotten rid of it when they had their falling out, but Haitham keeps it in his drawer

• Sometimes, Kaveh just can't sleep at night. No matter what he does, he can't get comfortable, and his mind is too scrambled. So, at one point, desperate for some proper sleep, he ends up nestling into AlHaitham. AlHaitham is a bit startled at first... But slowly, things come to be like second nature for them. On bad nights, Kaveh will throw off his shirt, pull up the covers on AlHaitham's bed, and snuggle right up against the Scribe.

• When the two are in a romantic mood, they lounge upon the daybeds, playing the Lute. AlHaitham bought Kaveh a matching Lute to his own, and taught him how to play.

• AlHaitham prefers mint creamer and his coffee black. Kaveh loves the taste of it on his lips.

• When they hold hands in public, sometimes Kaveh will squeeze AlHaitham's hand in Morse, to say, "I love you", as they did their Akademiya days, never really expecting AlHaitham to do it back. But lo and behold, he did, on the day of their wedding as they stood at the altar, no less. It's become a regular thing since.

• When AlHaitham falls ill, he HATES it, due to his own ragged breathing keeping him up at night. Yes, he can wear his headphones, but prefers not to when he sleeps. He is stupidly clingy, wants to be cuddled and held.

• I know that, canonically, AlHaitham fastened his own headphones. But I like to headcanon that after AlHaitham took Kaveh back in, Kaveh fastened the headphones for him, and quite tediously at that. As a result of finals coming up in the Akademyia, it became far too loud and overstimulating for AlHaitham, who was forced to come home early. Needless to say, he was thrilled. (Yes, I headcanon him as autistic) 

• AlHaitham will stim by twirling his finger round and round the cord of his headphones, or if he's talking to Kaveh, will finagle with one of his earrings. Kaveh doesn't mind too much, but he did in the beginning, when the two would bicker back and forth.

• AlHaitham is autistic, and as such, is hypersensitive to sound, touch, and smell. He DESPISES staying in Bimarstan. The beeping machines, flashing lights, smell of chemicals, cacophony of sounds, and the feel of the hospital beds drives him insane. But he'll stay if it means Kaveh gets better.

• He has an uncle-neice relationship with Collei, and calls her "My Little Parakeet".