In the Shadow Mirror universe, just like the original universe, Kyosuke Nanbu and Excellen Browning was involved in a shuttle accident triggered by the Einst. Unlike the original universe, Excellen died in that accident and was eventually resurrected without her memories as Lemon Browning, while Kyosuke ended up being turned into Einst in place of Excellen.
He would spend his life normally like the normal universe afterwards, but without the perky Excellen to counterbalance his stoicism, Kyosuke became more and more deluded into the Einst's goal, to destroy the world and recreate it anew. Along with that, he developed a nasty habit of messily murdering his opponents and sometimes even his allies. This change was extremely drastic that he eventually devolved into babbling nothing but his goal to recreate the universe in disjointed speech. Along with that, he started showing demonic powers that he ended up using to kill those who get in his way. With his squad, the Beowulves, he more or less controlled the corrupted EFA in the Shadow Mirror universe, to which his former teammate Axel Almer was disgusted and switched sides to the Shadow Mirror, only to stop him from further wrecking his world.
Original Generation 2
Beowulf is first seen during the prologue of the GBA version of OG2. At this time, nothing was known of him except his near-demonic power, but overall it was noted that this is more or less the same heroic Kyosuke. Axel stalled him so the Shadow Mirror can escape to the OG universe, a mission he succeeded. Beowulf wouldn't make another appearance afterwards.
Beowulf is spotted at the end of the 3rd mission of OG2 section of Original Generations, where it became clear that Beowulf is an Einst-possessed Kyosuke rambling about recreating the world in his image. His role is more or less the same and he is never seen again afterwards.
Original Generations: The Inspector
The first episode of the animated adaptation of OG2 showed Einst Beowulf's brutal nature, as he single-handedly annihilated and murdered the Shadow Mirror version of the SRX Team, before eventually confronting and was stalled by Axel. Unlike the game counterpart, Beowulf doesn't carry his own squad of robots, he works alone, it is implied that he probably murdered his whole squad for no reason in this continuity.
Axel used his new mech Soulgain to attack the approaching Gespenst Mk.III in hopes of allowing Lemon Browning, Vindel Mauser and their troops time to make the jump to the alternate universe. Initially Soulgain manages to gain the upper hand, obliterating most of the right arm of the Mk.III. It is then revealed that his world's Beowulf was more monster than anything else, sprouting Einst tentacles to regenerate the arm and turn his Mech into a monstrous Einst-construct.
Einst Beowulf clashes with Axel, melting part of Soulgain's ribcage. Axel counters with a full-body tackle against one of the beasts legs that has Beowulf crash down in the underground fortress housing the portal device. Axel disables the limiter and damages Beowulf's mech with Soulgain's signature Code Kirin.
He then activates the portal, stating Beowulf would remain here and die. This causes Einst Beowulf to suffer a villainous breakdown and charge Soulgain while the latter is already being enveloped by the portal. Axel fires Soulgain's Genbu Gokodan into the pilot's cockpit, seemingly mortally wounding Beowulf.
At the end of the series, just as the leader of the Einst (Stern Regisseur) is dispatched, it's body bursts into flames and a portal opens, expelling the still damaged Einst Beowulf, pilot and mech now one being. He intends to bring about the death and rebirth of the universe, believing himself a kind of perfect being. He summons four monstrous mechs, one original and three dark clones (of SRX, Grüngust Mk.I and Cybuster) to deal with his foes before setting a course for Earth. During transit he repairs and upgrades the fused form he inhabits, losing almost all of his once human features.
Fortunately, Guilliam Yaeger managed to transport several mechs (Granzon, Alteisen Riese, Rein Weissritter, Soulgain, Vaisaga.) through use of the gate system embedded in Zweizergain's head in front of the supremist monster. Alfimi and Axel sacrifice themselves and allow Kyosuke Nanbu to defeat his evil twin. His Revolver Bunker connecting with Soulgain's hand already embedded in the monster's torso opened up the vulnerable insides to the burning entry into Earth's atmosphere.
- Einst Beowulf was based off the Beowulf counterpart of mainstream Kyosuke Nanbu, but has not appeared as such in any game before the anime.
- Wendolo also received the same treatment for this series.
- His arrogant overconfidence is the key factor to his demise.