Minamoto game, year 1540, only one daimo left, Tachibana, who's vassal. Need to wait ~5 years to start diplo annexation attempts.
Bump. Ming offers RM. Accepted.
Ops. Several Ming provinces are occupied by rebeles, their stab is negative and, most important, their throne is free to claim. Being a sneaky and mean shogun/daimo who forged claims on half of Japan, I couldn't pass such opportunity.
To make it quick, several years later, under Regency Consil, I managed to force PU on Ming. But... They were in PU with JAPAN, not Minamoto. I didn't mind much and decided to proceed with Japanese unification. Few years of trying, and, while still under the same Regency Consil, Japan is united. Unfortunately, Ming PU is not transferred from original Japan to Minamoto Japan. Almost ten years of war, countless (from their side) and few (from our) armies destroyed, WE above 12, and constant rebelions has achieved nothing. Even less than nothing, since it slowed me for several years and quite a bit of money were spent on useless adventure. Plus, my precious new province China couldn't be defended from stray rebels and voltures, since no diplo actions would give me military access to Ming proper.
Angry as ... I re-loaded from prior to war. ~7 years passed, Japan is united, Ming is torn apart and lost a lot to Wu, relations are bad with both.
Conclusion? Don't play as daimo, Ming or the Hordes in DW. It's exercise in frustration.
Report this bug and I think PI could fix it. Doesn't seem too hard.
This is not a bug but a feature of DW: all communications of daimo with outside word go through Japan, whom can't be contacted by daimo. In this respect what happened is completely appropriate. Broken system with a patch is still a broken system.
to ywhtptgfo: I don't want to. Restarted from prior to war start savegame.
to Jos de Trol: Hordes missions, insta wars every 5 years, messed up historical vassals (when a Horde vassal can be overrun with impunity). My favorite are Formal Request to blobbed GH, and a mission Royal Marriage with Ottomans (or similar).