We don't know that yet, in fact we don;t even know all of the possible adults (one was just discoeverd yesterday). On the keitai, Dorotchi is like a hanatchi, so try caring for it like you would to get a hanatchi or robotchi and see what happens. I believe the connection V1 characters are available on the second generation, so you may be able to get it on the first or third. (I also believe there may be three sets of characters for three generations but I have not gotten enough evidence yet)