Harmony, before their death, connected communications and networked between ships. Their combat strength was tactical formations. Whereas most ships residents are 'chipped' in order to connect to the mesh, people in the Tides connect to the Mesh via nanites distributed throughout their bodies. Harmony was able to quickly communicate to their citizens because they were a part of them; Harmony was even able to take control of its Excerpts if necessary. It acted as a very good mediator, for citizens as well as those off-ship, and was a parental figure for the ships of the fleet.
While the cause of Harmony's death is unclear, people believe that they had spread themself too thin. Perhaps they were giving more nanites to more people in order to get more Excerpts, but got weaker and weaker as they gave more of themself away. As the population grew, Harmony eventually perished.
Harmony itself was shaped like a flower (a dahlia), and before its death it glowed with a bright light.