Miaplacidus

What triggers his illness

It seems likely that his condition is rooted in trauma— specifically, unresolved and possibly repressed experiences from his childhood?

His family, Zenji or also Taro, is a key trigger, I think. This COULD be due to his ongoing struggle with memory loss. (Like how he barely remembers anything from before or during the Clash)

His illness may be deeply embedded in emotional memory or trauma. I think it's connected to his childhood, since in one of his voicelines he states that he never formed strong emotional attachments as a child, particularly when it came to basic needs like food, comfort, or safety. That's NOT normal. This absence of connection and attention has probably shaped him as he is now: monotone, low emotional intelligence and described as apathetic and cold. He probably had no real bonds, atleast not in the way a child should. That isolation, whether due to neglect, trauma, or other circumstances beyond his control, may be the root of his illness.

Despite his amnesia, there are signs that his subconscious still holds onto the memory of his brother, or his family in general. I believe that those suppressed memories in him stir something within him every time he's reminded of them. Which, for him, is an attack from his own body. ↓

This is further supported in Chapter 17, when PC mentioned the current date, which happened to be Zenji's birthday, that Jiro's condition almost triggered again. ↓

His brows are furrowed and he gets sick, or almost. It's as if the memory of his brother reaches past his amnesia and strikes a nerve, possibly reminding him of his death? Similarly, in another chapter (The first interhouse chapter with Romeo, Kaito, Zenji and Jiro, the mere sight of that crying child triggered his illness.

He was even crying (I think) when this happened. This may be a far reach, but perhaps that child reminded him of himself? He IS the younger brother after all... Maybe Zenji used to help or support him throughout their childhood?

Connection to traumatic responses

Physical reactions to trauma can vary extremely.

Some symptoms are muscle tension, headaches, and aches. The muscles may tense up in response to perceived threats, which can lead to pain and discomfort.

Trauma can also disrupt the digestive system, (like in Jiro's case) causing stomach pain, nausea, or other problems.

The body may also be constantly on guard or, in some cases, the body may dissociate from the traumatic experience, leading to feelings of detachment or unreality– which is similar to Jiro's case.

Sensory information (sight, sound, smell, etc.) associated with the trauma could trigger a physical or emotional response, same for general information like dates or names, which is literally what's going on with Jiro whenever something associated with his past (family, especially Zenji) is mentioned.

Also, what I thought is most important for Jiro's case, is that trauma can be stored in the body's tissues and nervous system, even if the individual doesn't consciously remember the event or what lead up to it. This makes a LOT of sense! (Or maybe I'm just interpreting too much into it)

My Conclusion:

I think Jiro (and Zenji) both had a tragic past where they were severely neglected or exposed to some severe trauma– Zenji's death and the Clash for Jiro additionally. In response, Jiro has developed an illness, a traumatic response, to what happened. I think that, due to his childhood and potential negligence, he turned out the way he did. And due to Zenji's death, his illness worsened. It could be, that he suffered from a chronic illness since birth before, and his trauma response simply added some triggers to it.

What triggers his attacks? I think his memories, or flashbacks to certain events or people– really just memories, which are associated with negative memories from his past– trigger a severe trauma response which makes his own body attack itself.

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