You know, I'm kind of surprised that Nirlass didn't also get a happy end in Final Subjugation Target's SS2.
Because unlike the main story, where's Nirlass's main motivation was "I love trolling Kotone and seeing her suffer lmao", watching Kotone grow up from a baby changed Nirlass's motivation to "I want to become Kotone's mother (and I'm jelly as fuck of Kagami)".
She literally doesn't do a single bad thing to Kotone until the final arc and all the powers she gives Kotone come without any strings attached unlike the main story (besides needing her to bleed out as a basic requirement). Even in the final arc, the antagonists for the most part were the glowies relentlessly hunting down Kotone until she had no choice but to summon Nirlass to deal with the situation, and Nirlass only ended up fighting the rest of the cast because they didn't agree with Kotone's wish to trap them in a dream world where they could be safe and happy forever and tried to drag her back kicking and screaming. Even after they "defeat" her and she fucks off Nirlass does them one last solid and brainwashes all the glowies so they start chasing some illusionary Kotone around the world while leaving the real one alone.
Like she was as heroic as an Outer God can get in this side story.
To be honest I halfway expected her to just hijack the rest of Koko's meat and create another human vessel that looks like Kagami to larp as Kotone's second mom in the epilogue or something.