I know people with DID so I’m just going to based off my observations, but DID is recorded to often present itself differently for people and I don’t have a personal experience of this disorder so I can be totally wrong. But from my understanding, it makes sense that Hosu was his bubbly as a 5 year old. Since the disorder occurs by disassociating the personality into different identities to cope. There’s usually a primary personality, but there’s no original self because these identities are fractured off once was a whole personality. Identities can develop different interests and preferences, but their base-line self comes from the same core. Disassociating is essentially being on autopilot, so the dissociative identity disorder is being on autopilot very long that it develops a new ego(s).
Sorry if this doesn’t make sense, it’s the first time I’m actually putting my observations of this disorder into a cohesive explanation. I’m also not in a psychological field so someone with actual academic knowledge, please correct me.

Does the special 12.5 chapter have any canon part regarding Hosu’s DID? His 5yo self seems to be akin to the bubbly version of Hosu, yet in chapter 13, the “primary” Hosu says he was there before the bubbly version. Just wondering