I know KRI55E from Planet VB tried contacting him with a Japanese acquaintance and got no response. Shame, because I really want to know more about DH, too. I have a good feeling it was complete, but if it wasn't, I will be very disappointed, as it is the only unreleased game I am desperate to play, but if it never was completed, I probably won't have any other holy grails to look forward to, as my other (but lesser interests) like Sonic 1 proto and Twelve Tales: Conker 64 would be interesting but ultimately incomplete as well!
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Govinda jaya jaya, Gopala jaya jaya. Blessed Krishna, save us!