This is just an excuse to project chronic pain on Tsukasa. Originally considered just giving Saki a physical disability instead of illness, but idk it felt wrong? Like that would fundamentally change her experience by changing it.
So yeah, Tsukasa was born with a misshapen spine (based on spina bifida, except the part that you can tell someone has it from birth) that causes severe pain, especially in the back, along with weakness and lack of sensation in the legs and lower back area. Also when he was younger, before Physical therapy, his legs would sometimes give out on him
Before his legs stopped working for the first time, his parents didn’t take him seriously about the pain he was in, they weren’t being malicious just typical non-recognition from able bodied people. So he spent awhile thinking what he was going through was normal and kinda permanently internalized the idea that any pain that wasn’t entirely debilitating was just something to work through-
Of course once his condition was discovered, he spent a lot of time in and out of the hospital with the amount of surgeries he needed along with mapping plans for his future. E.x, treatment plans including projected support needs based off his current condition, what level of mobility aids would he need at all times based off his, well, mobility and of course what type and how much physical therapy he would need in the moment and moving forward.
While it ends with Tsukasa having the core strength of a god, PT (physical therapy) at the start was Hell. Since he had little to no strength at the start, even doing something as simple as leaning forward was incredibly painful. A combination of pain along with frustration of not being able to do incredibly basic movements is hard for anyone to deal with, let alone a child, so it’s really no surprise Tsukasa hated the PT and also tended to completely lose his chill during sessions- Honestly if young Tsukasa knew curse words he’d be a damn sailor!
(Side note anyone who says canon Tsukasa would be anything but strong obviously have never done stunt work or dance. Mans got that lean muscle, do not discount him because he’s a theater nerd and not a jock)
He still plays piano and wants to become an actor, his mom was teaching him piano before his disability was known and it was one of the few activities he enjoyed that he could still do reasonably well while not pushing himself. Except the whole posture part, he can’t sit up straight because of how his spine is bent, so he uses the piano itself to push himself upright, yes he’s very bad at playing softly.
Still he becomes quite skilled since he spends so much time playing and ends up bonding with saki over it. As she says, he would play with her for however long it took her to figure it out and whenever she was able to play the whole thing right, he’d smile at her so genuinely Saki believed that maybe for that little bit he’d forget about his pain. That’s what inspired her to not only learn piano as best she could, but also write music. So there’d always be a new piece to perfect and make her brother smile.
Of course since Saki goes to school normally, she has access to her piano a lot more and is more proficient at playing and making music by the time leo/needs story happens than in canon. Also she definitely plans to go pro, she wants to create music that makes you momentarily forget all the bad things in life and share it with everyone!
Tsukasas reason for wanting to be a star is the same as canon, except it’s about how the star made everyone, including himself, smile for real and made his family happy, washing their worries away. So he wants to be a star to make his family smile in genuine happiness around him, instead of strained and worried smiles.
When WxS story takes place, Tsukasa is not going to school and is instead enrolled in online classes. Partially to suite how often he needs to be in the hospital, but also because none of the nearby schools are particularly accessible- by this point Tsukasa has enough mobility to be able to walk without aids for short periods of time and otherwise mostly use crutches, although he does have a walker for bad days and also for holding stuff. But that’s on generally flat ground, having to walk up and down stairs in a school setting would be decidedly Bad.
Other small details: Wonderland Sekai is slightly changed, the floor is all clouds which are super soft and easy to walk on, and the gravity in the Sekai is noticeably lighter which makes walking a bit easier on someone who’s constantly weighing down on themselves because of spine problems.
Tsukasa still has memory issues, but it’s hard to see them as a real thing when it makes sense that days of doing the same things kinda just bleed together. They are still a problem, just harder to recognize.
Due to weakened sensations in his legs, Tsukasa has a lot of little scars on them from not being able to feel when he’s gotten injured.
I do have WxS general story arch laid out, but this is already getting long so I’ll make that another post (if people want it?)
All I’ll say about it is, the troupe do Not know about Tsukasa’s disability for a good bit of it and it will cause problems™️