... not a bad theory actually...

And Mal looks tough in that training getup!

Right?

So far Katsumi has only been a thoughtform in Jin's head and was confirmed not to be schizophrenia or a hallucination from a mental illness. I feel like the latter mention has ruled out Dissociative Identity Disorder entirely, and that's further supported with how they are both active consciousnesses. I mean Jin and Katsumi have had conversations with one another.

It's yet to be revealed if Jin can communicate to Katsumi using a mind voice. Most of the endrogenic systems Mal and I have met speak through our mind voice, but that's not at all required. If Jin speaks to Katsumi aloud and she responds via mind voice, that could still lead credence to her being a tulpa.

If Katsumi is able to physically interact with the world, that would nullify her from being a tulpa, but that borderlines magic territory which Twin Dragons hasn't had (it's been very grounded in reality). Regardless, it's nice to see some representation. I really speculate there are lots of tulpas out in the world people aren't open about, given the practice (and hearing voices in general) has cross-cultural and religious occurrences. I'd even go so far as to say Christians who speak with god (see "When God Talks Back" by Dr. Tanya Luhrmann) may have formed a type of tulpa, which is somewhat ironic since tulpas were originally a concept defined by Tibetan Buddhists.

More to the point - Japan has a very active tulpamancy community (Tulpas translate to タルパーズ or "tarpa" in Japanese) that's been posting on forms and writing guides far before the western guides were written. I believe one of the first western guides was a translated Japanese guide. Going back to Buddhism - 67% of Japan's population practice Buddhism, and I feel like that goes well with Jin's character, even if Japanese people do not necessarily practice the Tibetan variant (Japan and other Asian countries follow Mahayana Buddhism, Tibet follows Vajrayana Buddhism). We'll have to wait and see how Jin and Katsumi develop to make any kind of determination, I suppose.

...Sorry, that theory went on longer than anticipated.
Mal's ready to fire a hadouken! ...Or at least, try to.

Also something worth mentioning - Martial arts are claimed to originate from Tibet. ^^
Jin hasn't been shown to use it to fight, only for self-defense, without harming the other people at the dojo he used his teachings.

And the theory is even better when you flesh it out! Nicely done, I can totally see how it would have merit!

Althought still, only one knows the truth, and he ain't telling until the right time :D