Vivimustdiee

they’re both terrible at feelings but great at loving each other

*butchbeams sanemi*

Sensory issues - He is canonically sensitive to sounds. He also displays other sensory issues--see his extreme reaction to Aoi forcing medicine on him during the Rehabilitation arc. It very much reads as someone having a sensory reaction due to the bad taste/texture. Zenitsu also likes the sensory input of physical contact--there are several moments where he craves physical touch, such as him clinging to people or when he giggles when the Butterfly triplets stretch him. While yes, some of this is due to trauma from being unloved and abandoned his whole life (and touch starved), that doesn't totally discount this from being an autistic trait. Additionally, you can be both traumatized and autistic.

Meltdowns - Zenitsu has frequent loud meltdowns that tend to leave him stuck in his own head. He also has virtually no emotional regulation skills, and frequently experiences extreme dysregulation.

Anxiety - While not an autistic trait on its own, a lot of autistic people do experience high levels of anxiety and anxiety is commonly comorbid with autism. Zenitsu has extremely debilitating levels of anxiety.

Stimming - There are multiple point in the series where Zenitsu stims. When he first meets Tanjiro, he's in the middle of a meltdown and physically bridges his body upwards multiple times (physical stimming). When angry at Tengen during the EDA, Zenitsu loudly (and flawlessly) strums on shamisen (both physical and auditory stimming). His frequency in clinging to other characters--usually Tanjiro--also qualifies. He clings to Tanjiro in order to ground himself (tactile stimming). When distressed, he does a lot of yelling or screaming (vocal stimming).

Atypical social behavior - Zenitsu's social skills are genuinely awful. He has trouble making friends and forming bonds, and it's implied Tanjiro was his first friend in his entire life. Other characters that are not in Zenitsu's immediate circle view him as weird and annoying (reality for autistic people). Zenitsu misses social cues and has trouble picking up on boundaries in canon, but is genuinely apologetic when he realizes he's overstepped or made someone uncomfortable. He puts in an effort to change his behavior when he's called out.

Atypical levels of empathy - Zenitsu is genuinely very compassionate and kindhearted, and want to protect and help people. However, he does struggle with cognitive empathy. He gets so stuck in his own head that he fails to pick up on others' emotions, and does sometimes struggle to see where others are coming from (ie, he struggles to put himself in others' shoes). This is what empathy actually is--it is not the same thing as compassion, and has nothing to do with being a good person. Even with his hearing, this is a struggle for him--Zenitsu receives the social data, but struggles to interpret it correctly.

Strong sense of justice - A strong sense of justice is common in autistic people. Zenitsu, despite his fear and anxiety, refuses to abandon Shoichi in Tsuzumi Mansion, and takes steps to protect him (he actually encourages Shoichi to abandon him). He puts his life on the line to protect Nezuko's box simply because Tanjiro (who he considered a friend) said it was important. During the Entertainment District arc, he joins Tanjiro and Inosuke in standing up to Tengen when Tengen posed a threat to Aoi and Naho's wellbeing. During the same arc, he stood up to Daki (who he knew was a strong demon) when Daki was abusing a little girl, simply because Zenitsu could not stand the way Daki was treating her. He also later demanded (in Sleep Mode) that Daki apologize to the girl she abused. And when Kaigaku betrays the Corps and causes Jigoro to commit seppuku, Zenitsu is so enraged that he finally pushes past his debilitating anxiety and focuses on nothing but bringing Kaigaku down.

Volume control issues - Zenitsu is loud without meaning to be, particularly when he gets upset or excited. This is common with autistic people.

Hyperfixatioins/SpIns -- Zenitsu has a fixation on Tanjiro and Nezuko. He hyperfixates on them because they are his safe people. The reason he clings to them is because they represent safety and unconditional love and acceptance, which is something he deeply craves. He also not only mastered the first form of Thunder Breathing, but mastered it to unprecedented levels, and failed to learn anything beyond that (despite trying). This brings to mind overspecialization found in autistic people when they focus on One Specific Thing and get really good at that thing, but not much else.  Even the form he invents later on is extremely similar to the first form.

Bluntness - He lacks a filter and tends to run his mouth (especially during moments of high anxiety.  He tends to be brutally honest about the situation (and the behavior of his friends), but isn't mean spirited.