I think you're supposed to defeat 5 snake onigoes before going through.  Check your quest list.

In the Grimoire Palace, I think, there's an onigo that reflects physical damage and I cannot, for the life of me, how to figure out how to beat him.  I have tried capturing it but I keep missing.  What's going on?

<t>I don't know if this might include possible spoilers for part of the game but I desperately need help on this part and I can't find a walkthrough to explain it all for me.<br/> <br/> I am trying to get further into the castle to find Ishtar and Ramires.  I got the moon key and opened up part of t...

I just started on Dragon Sinker and now with Dragon Lapis as well.  I hope to see more of these kinds of games in the future.