U-Mos is the last living Sentinel of the Luminoth during the events of Metroid Prime 2: Echoes. His mother, V-Mos, was also a Sentinel, but died giving birth to him. After the Luminoth were defeated by the Ing in Agon Wastes, Torvus Bog, and Sanctuary Fortress, they fled to the Great Temple and placed themselves in stasis; U-Mos stayed awake to guard the Great Temple's Energy Controller and the sleeping Luminoth.
The Arrival of Samus
When Samus defeats the Alpha Splinter in the Great Temple on Aether and meets U-Mos for the first time, he beseeches her to listen as he explains the nature of his planet's peril. He tells Samus that a cosmic object impacted the planet's surface and caused a rift in time and space, plunging Aether into Transdimensional Flux and resulting in a Dark Aether. After explaining the war with the Ing for Aether's planetary energy, he tells her that the technology called the Energy Transfer Module has bonded to her Power Suit and implores her to aid him in repelling the Ing forces. When Samus agrees, U-Mos becomes her guide. He gives her basic instructions regarding acquiring planetary energy from the temples on Dark Aether, updates her map system with the location of a temple in Agon Wastes, and updates her Translator Module.
After Samus is successful in returning the planetary energy from Agon, U-Mos directs her to Torvus, and after she returns the Light of Aether to Torvus, he directs her to the final Luminoth stronghold in the Sanctuary Fortress.
Once Samus returns the Light of Aether to all three Luminoth Temples on Aether, U-Mos asks Samus to find the nine Sky Temple Keys required to enter the final Ing stronghold and gives her a blessed suit of armor known as the Light Suit.
U-Mos is last seen after Samus destroys the Emperor Ing with his fellow awakened Luminoth; he and the others bow in respect as they bid her farewell.
- U-Mos will sometimes summon a sphere of light in one hand, attracting a swarm of moths.
- "This is a statue of V-Mos, the third Sentinel of Aether. She died giving birth to her son U-Mos, who, in time, became the fifth Sentinel of Aether." —Scan Data (Metroid Prime 2: Echoes)
- "Subject is U-Mos, a Sentinel of the Luminoth. Scans indicate numerous beneficial abilities, including heightened reflexes, durability, psionics, and flight. Ability to generate and manipulate energy on par with that of the Chozo. Dating scans suggest an age of 2.15 centicycles. Only known active member of the species: remaining Luminoth locked in protective stasis until crisis is resolved." — Logbook "U-Mos" (Metroid Prime 2: Echoes)
- "What few remained gathered in the Great Temple. There, all but U-Mos, the last Sentinel of Aether, entered into life-preserving stasis. There they remain, to be released once the Ing were destroyed...or to sleep forever. His people safe, U-Mos prepared for the last, terrible assault. In the silence of the Great Temple, he prayed for salvation, for deliverance from the terror of the Ing" —Metroid Prime 2: Echoes Logbook "Twilight" (Metroid Prime 2: Echoes)
- "Do not be afraid, I am U-Mos, Sentinel of the Luminoth. Please listen, and hear of our world’s peril." —U-Mos (Metroid Prime 2: Echoes)
- "Long ago, a cosmic object fell to our planet, Aether, exploding with great force. A rift was torn in time and space, and a strange power flowed over the world. Where once there was once Aether, there were now two. One of light…and one of shadow, each existing in its own dimension." —U-Mos (Metroid Prime 2: Echoes)
- "It was the end of peace on Aether, for a new race was born that day on the dark world…one filled with hate and terrible power. They are the Ing. The Ing are creatures of shadow and darkness, knowing nothing of peace or mercy. For decades, we stood against them…yet we now lie on the verge of defeat. When Dark Aether was born, our planetary energy was divided. Half for our world, half for theirs. Should one world gain control of this energy, the other will perish. Before you arrived, the Ing had stolen a device from us…one that collects planetary energy. With it, they have weakened our planet to the verge of collapse." —U-Mos (Metroid Prime 2: Echoes)
- "But fortune smiled upon us this day, for the Energy Transfer Module…is now bonded with you. With it, you can help us…help us restore our world. You’re our only hope, Samus. Should we fall, the Ing will look to the stars for new planets to ravage and conquer. Your species could be their next victims." —U-Mos (Metroid Prime 2: Echoes)
- "The Ing have taken our energy to three temples on Dark Aether. Find these temples, and transfer the energy from them to our own. I have updated your map system with the location of another temple. There is knowledge there that can help you on your way. I have also updated your Translator Module. You can know access devices and doors coded with Violet holograms. Many lands are now open to you. Prepare well for your journey. The Ing now know you possess the Energy Transfer Module. They will try to recover it at all costs. Return to me once you have restored the energy to a temple. I will aid you as I can. May the Light of Aether shine upon you!" —U-Mos (Metroid Prime 2: Echoes)
- "The temple in Agon’s dark shadow holds what you seek. Return the missing energy, before Agon is lost forever to the Ing." —U-Mos (Metroid Prime 2: Echoes)
- "I thank you for restoring energy to the Temple of Agon. Your valor honors the Luminoth…those who have passed, and those who remain…here, under my protection as they sleep in a deep stasis. Be on guard, for the Ing do not suffer defeat lightly. They will surely seek revenge for your actions. With the energy lost from the desert region, they will increase their efforts in other lands. I have detected unusual amounts of Ing activity in the Torvus sector. The enemy is on the move. The swamplands of Torvus are treacherous, and can hinder you considerably. Bear this in mind as you move through the bog. Seek the Temple of Torvus. More knowledge awaits you there. May the light of Aether serve you well!" —U-Mos (Metroid Prime 2: Echoes)
- "The temple of Dark Torvus holds more of our precious energy. Return it to us and restore life and order to the Torvus Bog." —U-Mos (Metroid Prime 2: Echoes)
- "The Temple of Torvus glows with energy once more. Only one temple remains without the Light of Aether. You must travel to our fortress, high in the cliffs. The last temple lies in the fortress. Seek knowledge there before invading the Ing Hive. Be cautious in the fortress. This place was once guarded by machines of our creation, but now they are corrupted slaves of the Ing. They will not see you as a friend. Our goal draws ever closer. Let the Light of Aether be your guide." —U-Mos (Metroid Prime 2: Echoes)
- "You have weakened the enemy forces in Torvus. The Ing now fear and loathe your name. Do not relent. Press on! Show the darklings in Sanctuary no quarter!" —U-Mos (Metroid Prime 2: Echoes)
- "The Light of Aether shines from all three temples once more. And yet, Dark Aether remains. One Energy Controller still shines in the darkness, sustaining the world. The Sky temple, dark shadow of this hallowed place, holds the final Energy Controller. The greatest and most powerful beast of the Ing keeps guard over what you seek. The nine keys to the Sky Temple have been hidden in each land of the dark world. Finding them will be perilous, but… …I offer you this blessed suit of armor, energized by the Light of Aether itself. Its power will help you reach these final keys. May it serve you well in the darkness!" —U-Mos (Metroid Prime 2: Echoes)
- "The last stronghold of the Ing remains. Seek its nine keys to gain entry. Once you reach the Sky Temple, let nothing stay your hand!" —U-Mos (Metroid Prime 2: Echoes)