I didn't think I'd ever see Voss Parck again after I left the Empire behind, except perhaps as an opponent in battle. But, here was me, him, and my sister, sitting at a table together, politely discussing potential threats to the galactic security and stability.
—Arius Valdayn regarding the Accords' negotiation
The Nirauan Accords, also known unofficially as the Demesnes-Hand Treaty, was a secretive, semi-official diplomatic agreement signed by leading representatives of the Ethereal Demesnes, Ethereal Empire, and Empire of the Hand. While neither the Demesnes nor the recently-resurrected Empire officially recognized the Empire of the Hand, owing to their existing relationship with the Chiss Ascendancy, unofficially both the Ethereal and Chiss leadership acknowledged the benefits of working with the secretive state established by Imperial Grand Admiral Thrawn. The Ascendancy had, in fact, already worked with them militarily, but the Ethereal state had refused to do so owing to hostility to Thrawn himself as an Imperial leader.
In 10 ABY, shortly after the end of the Thrawn campaign and restoration of the Ethereal Empire, the Hand of Thrawn played host to arguably the two most powerful Ethereal Humans alive at the time, the twins Arius and Atheria Valdayn. The pair met with Hand head of state Voss Parck there in-person, negotiating the terms of the secretive, not-quite-official agreement which, upon their return to the Ethereal Demesnes, was quietly ratified in lame duck sessions of the Diet of the Ethereal Demesnes and Ethereal Senate. While the Demesnes and Empire never officially recognized the Empire of the Hand as a legal state, they did provide assistance to and work with the Hand on several occasions, pursuant to the terms of the Nirauan Accords.
While the Galactic Civil War still raged in the greater galaxy, elements of the Demesne Defense Forces, the Ethereal Military, the Chiss Expansionary Defense Force, and the Hand's Household Phalanx gathered together in efforts such as combating the Ssi-ruuvi invasions and the Camskarlund Skirmish. More notably, the four gathered together to protect the Unknown Regions during the Poltiyir Incursion, which led to the only joint Demesnes-Empire-Ascendancy-Hand occupation and scientific expedition in history. In spite of these joint efforts, it is uncertain if the Ethereal Demesnes ever authorized official diplomatic relations with the Empire of the Hand, as they continued to value their relationship with the Chiss Ascendancy significantly more than that with the Hand, going on to revise the Ethereal-Chiss Treaty almost three decades later to further that relationship.