[ ] Protectorate: Aid will be provided on the condition of the Crystal Empire becoming a Protectorate of Gryphus. While the Crystal Ponies will be allowed a degree of autonomy over their own affairs, they will be considered a part of the Empire. A portion of their tax revenue will be paid to you, and they will be protected from outside aggression by the might of the Imperial Military. The vast majority of Crystal Ponies would be content with this, not believing themselves capable of standing on their own hooves so soon after their liberation from Sombra, and seeing the assistance gained as being well worth the price of some of their autonomy. And while some of the particularly ambitious members of your nobility may grumble a bit, most of your own people will likely see this arrangement as beneficial. Though it should be noted that the attitudes of the Crystal Ponies may change with time, either seeking independence or further integration into the Empire itself. Something to think about at any rate.
[ ] Naval Base: A plot of land along the Eastern Coast will be "leased" to the Neighponese for the next century. While the Crystal Empire will retain ultimate sovereignty over the land, the Kingdom of Neighpon will exercise complete control and jurisdiction over the land itself. The land will be used solely for military purposes, and will not engage in resource extraction or serve as a civilian settlement. While neither party will be particularly happy with this compromise, neither will particularly disapprove. Some few Crystal Ponies actually like the idea of having a foreign military base nearby to serve as a deterrent to any foreign aggression.
[ ] Joint Custody: While the Heart will remain within the Crystal Empire, it will be under the shared control of the Crystal Empire and the Empire of Gryphus. This will allow you to study and make use of the Heart more or less freely, though the Crystal Ponies reserve the right to protest a particular course of action if they feel it threatens the Heart itself. Most Crystal Ponies would be perfectly fine with such an arrangement. So long as the Crystal Heart remains in the Crystal City and continues to serve as the guardian of its inhabitants, they are fine with whatever experiments you may decide to run on it.