The Luminoth first encountered the Ylla while roaming the vast expanse of space. The deep bond the Ylla and other races had formed with their respective homeworlds inspired the Luminoth to claim one of their own, and several cycles later they settled on Aether. They recorded their encounter with the Ylla in their historical lore.
The Bryyonians encountered the Ylla after sending spaceships in all directions from Bryyo during their Age of Science. A friendship was forged and they commenced trade of wisdom and technologies, and records of their encounter were left in the form of Bryyonian Data.
- The name Ylla was misspelled "Vlla" in the first release of Metroid Prime 3: Corruption, but was corrected with the release of Metroid Prime: Trilogy.
- "It is told that the Luminoth were not born of Aether, but of the stars. In the early days, we roamed the greatness of the void, bathing in the glorious light of a thousand stars. We met a vast number of enlightened minds... the N'kren, the Ylla, and the Chozo among them. Each of them, we found, had claimed a homeworld and formed a deep bond with it. In time, we decided to do the same." —Luminoth Lore (Metroid Prime 2: Echoes)
- "The ships of Bryyo sped to the stars, in all directions, bearing the banner of peace. Soon we found stellar brethren in the Chozo, the Luminoth, and the Ylla. Starborne knowledge came to Bryyo, and we gladly sent our wisdom to our new friends in return. The hearts of Bryyo were filled with pride, and they honored the Lords of Science for all the wonders they provided. As the time of New Bryyo came to be, the old ways faded. The cries of joy from those who honored Science covered the angry shouts of those who mourned the old ways, the Primal Traditions." —Bryyonian Data (Metroid Prime 3: Corruption)