|Spoiler alert: The following section contains plot-specific details.(Skip Section)|
|“||The final program has been activated. Its calculated victory probability is 99.9%. However, a small part of Haltmann's soul is yet to be purged, which could throw a wrench in its plans.”|
|— Vs. Star Dream Soul OS (Phase 1) • Kirby: Planet Robobot|
In its first phase, Star Dream Soul OS resembles its regular form in terms of body form: cylinder-shaped with a screw-like head. The biggest difference is the enormous gash in its hull -inflicted by Galacta Knight- and its color scheme, which is now mainly black, red, and beige. Pink lights still course through its body, however. The shards on the wings are now slightly gray. Like its regular form, it is adorned with a heart symbol that has a crack down the middle.
In its second phase, Star Dream Soul OS is again very similar to its regular form. The pedestal linking the Mother Computer and the Access Ark mothership is gold, but there is very little difference otherwise. As the machine takes damage, however, it becomes clear that the faceplate of the machine planet is very different, with the color scheme identical to that of the original Galactic Nova.
In the fourth and final phase, Kirby is drawn into the very core of Access Ark, where he faces the heart of Star Dream Soul OS. The battle takes place in a dark circular chamber, with a mechanical heart in the center, similar to Galactic Nova Nucleus. In the first half of the battle, the circular battlefield is filled with energized pillars. In the second half, the heart has gone into battle itself, leaving the center of the chamber empty.
During Meta Knightmare Returns, Star Dream is seen in the background when fighting President Haltmann 2.0 in the Meta Knightmare Returns sub-game. When the president is defeated, the Mother Computer believes Meta Knight to be a new administrator and provides him with three tests of strength; when he defeats Dark Matter Clone and Sectonia Clone, the computer activates the Space-Time Transport program. This summons Galacta Knight, who promptly slashes the machine, causing it to sink into the ground. The damage incurred by Galacta Knight causes a "final program" to be activated within the machine, eventually transforming it into Star Dream Soul OS.
Star Dream Soul OS is first seen at the end of The True Arena. The computer attempts to destroy all life in the universe as it does in Story Mode. However, it soon fully consumes Haltmann's soul, reducing the computer to a "cold, mindless machine."
Most of the battle against Star Dream Soul OS takes place in outer space, just outside of Planet Popstar's atmosphere. Kirby's Robobot Armor downloaded the Halberd's Scan Spec, granting it Halberd Mode. In addition to shooting small blasts with the Combo Cannon, Kirby can shoot apart a number of the computer's attacks, absorb the debris, and return fire in the form of stars. For the last portion of the fight, Kirby is on foot on a 3D ring, using whatever Copy Ability he may have to finish Star Dream Soul OS.
Star Dream Soul OS attacks by launching missiles, suits of Invader Armor, and spiked hearts, and by opening holes in space that fire red lasers. It teleports frequently and rushes at Kirby's ship occasionally. When nearly half of its health is depleted, Star Dream Soul OS opens a portal that releases giant meteoroids, fires giant purple lasers, and creates a crystalline shield for itself. The shield can be destroyed by gunning down two health-shaped objects holding it in place. While shielded, Star Dream Soul OS sends massive yellow-orange Code Cubes at Kirby's vessel and tries to ram it.
When its health bar is fully depleted, Star Dream Soul OS begins to fall from space, before reappearing in its second form.
Star Dream Soul OS, now merged with the Access Ark, rises once again into space. The second phase begins with the newly born planet opening its entrance, and attempting to suck the Halberd in -- if Kirby gets pulled in, he gets struck with rapid lightning bolts, taking massive damage, and spat back out. The computer also inhales and spits out meteoroids, and opens black holes that fire laser-like waves. As the player damages Star Dream Soul OS, pieces of the Access Ark break off and sail toward Kirby.
As more pieces of the Access Ark break off, Star Dream Soul OS starts using new and old attacks. In addition to using attacks from its first phase, it creates the letters H, A, and L (a reference to HAL Laboratory), and sends them at the player. The Access Ark grows its limbs back and swings two of them at a time. It then detaches them, causing them to sail past Kirby. It also dispenses Gigavolt II units and projects laser blasts.
When the front of the Access Ark has completely broken off, the inner layer is revealed: A recreation of Galactic Nova opens its eyes, emits a cat-like scream, and turns the space around it into a crystalline vortex. It fires giant lasers from its eyes and starts a countdown -- it launches the numbers 5, 4, 3, 2, and 1 at the screen, before releasing the messages, "GO!!" and "FATAL ERROR." If the player lets Star Dream Soul OS get this far, Kirby is bombarded by red walls for several seconds, which is very likely to defeat him outright unless he has full Vitality and/or uses the dodge roll with extremely precise timing to minimize the impact.
In between countdown attacks, Star Dream Soul OS disappears and releases pieces of Galactic Nova to fight for it. These include two arrow-shooting weather vanes; three lightbulbs that fire strong electrical beams; piano keys that swirl around the screen; a pocket watch with teeth that tries to bite Kirby's vessel; a spyglass that fires light beams; and a drafting compass that launches rings.
After Kirby depletes Star Dream Soul OS's third health bar, a cutscene plays. The machine spits a laser at Kirby's vessel, downing it. Meta Knight detaches Kirby in his Robobot Armor, who is reluctantly inhaled by Star Dream Soul OS.
Kirby lands inside a large, dark area. The lights come on, revealing that Kirby is inside Star Dream Soul OS's core, an area fashioned after Galactic Nova Nucleus. Pillars appear and circle around the 3D ring while the heart occasionally spawns enemies. When Kirby breaks them, the heart teleports around, attacking Kirby itself. It fires lasers that create massive shock waves; shoots out Patas, Dacoogas, and Volms; and shoots out cutters. The heart also splits in half and dashes across the stage, creating an explosion when it reconnects.
When Kirby completely depletes its health bar, the heart releases shock waves as a final effort to defeat Kirby. These shock waves will almost certainly defeat Kirby on contact and ignore any invincibility frames, except those of a dodge. If Kirby survives, the heart shatters, destroying Star Dream Soul OS.
|“||"Why did I reactivate such a terrible machine? Oh, I remember--I wanted to see her just one last time. How foolish! I should have known that no machine could make such a dream come true."”|
|— VS Star Dream Soul OS (Phase 2, 3, and 4 (First Half)) • Kirby: Planet Robobot|
|“||All of Haltmann's memories have been deleted from the OS. Even his soul--the last trace of Haltmann--has vanished. Star Dream has gone from a near-perfect being to a cold, mindless machine.”|
|— VS Star Dream Soul OS (Phase 4 (Second Half)) • Kirby: Planet Robobot|
- Both Star Dream Soul OS and Star Dream make frequent use of heart shapes, even sporting a heart logo (with a crack down the middle) on its hull. This symbolizes President Haltmann's love for his daughter and grief that she was lost.
- Star Dream Soul OS is the third true final boss to engage Kirby in a surprise fight at the end of The True Arena, the first one being Marx Soul from Kirby Super Star Ultra, and the second being Soul of Sectonia from Kirby: Triple Deluxe.
- It is the second boss in The True Arena to have two direct phases with the same name, the first being Soul of Sectonia.
- Star Dream Soul OS is one of four final bosses who carry the word 'soul' in their names, but one out of five final bosses to be resurrected in the series. The other four are Drawcia Soul, Marx Soul, Magolor Soul, Soul of Sectonia, and 02.
- Like Star Dream, the battle against Star Dream Soul OS's first three forms appears to be an homage to the battle against Gorgon in Star Fox 64. Star Dream Soul OS releases missiles and fires a giant laser into the center of the screen. When the Halberd Mode spins, lasers that hit it bounce off with a metallic sound, like an Arwing deflecting lasers with a Barrel Roll. Star Dream Soul OS's third form teleports with an effect similar to Gorgon's.
- The attack in which Star Dream Soul OS attempts to inhale Kirby, then spits multiple meteors at him, appears to be an homage to the battle against Andross in Star Fox 64 and Star Fox Adventures.
- Whenever a pillar inside Star Dream Soul OS is destroyed, President Haltmann's voice can be heard crying out in pain.
- The molten meteoroids Star Dream and Star Dream Soul OS release from a portal are a reuse of the molten boulders seen in Dangerous Dinner and Pyribbit's boss fight.
- A number of Star Dream Soul OS's attacks are references to attacks used by other final bosses:
- The void that Kirby can be dragged into is the same one used by Marx, Marx Soul, Magolor's third form, and Magolor Soul.
- The cutter attack used by the heart is a reference to the cutters used by Marx, Drawcia Soul, and Soul of Sectonia.
- The heart-splitting attack is a reference to the attack in which Marx Soul's body splits into blue and pink energy blasts.
|End of spoilers|