Attached here is the powerpoint file I used in my presentation at the Cyberspace 2016 conference on 26 Nov. 2016.
I examined the Tokyo District Court's decision in a suit filed after the opening of Mt.Gox's bankruptcy proceedings. The suit was filed outside the bankruptcy proceedings to obtain a full recovery of the bitcoins of which the claimant had a contractual right to return from the bankrupt exchange. To do that, he sought rei vindicatio of the bitcoins over which he asserted ownership rather than making a contractual claim to join other creditors in the bankruptcy proceedings.
I considered three questions noted at p. 4 of the slides. On the first question, the Court relied on the Japanese law concept of "shoyuken" to deny that bitcoins could be an object of ownership. But if we leave aside the technicality of the Japanese law concept and understand the concept of ownership more broadly to mean a right to monopolize the exploitation of objects, it may be possible to say that bitcoins are fit to be an object of ownership. This would open the possibility of rei vindicatio, if other prerequisites are satisfied. The other two questions I considered relate to those other prerequisites. In most of the cases, a customer of a bitcoin exchange would have difficulties meeting those other prerequisites but the possibility of a successful claim is not foreclosed in all cases.