|WARNING: This article contains spoilers for the alternative routes of OMORI.|
"Sunny... If you won't face the truth... then face me. Face the suffering you've caused for the people you love... The pain of knowing what you've lost... And the hatred of yourself for being too cowardly to change anything about it... Let these feelings devour you here... until your insides rot."
-Stranger calls out Sunny for his refusal to face the truth, immediately before he attacks
On the Hikikomori route, Sunny doubles down on his repression of the truth, rejecting his last opportunity to see his friends and instead focusing on the to-do list his Mom left him. As a result, he becomes reliant on Headspace as a coping mechanism, and without the support of his real friends, he begins to lose himself completely.
This reaches it's culmination in Black Space. When Omori scales the Church Of Something area, instead of executing Basil, he will instead attempt to save him, as Sunny has shown no desire to reconcile with the truth. Before they can go anywhere, however, Stranger will approach the two, questioning how long Sunny will run away from the truth. Summoning Something, Stranger quickly consumes Omori, and forces Sunny 'out' of him, leaving them alone in a dark abyss. In a last ditch effort to make Sunny acknowledge the truth, Stranger demands that Sunny 'faces him,' to force him to acknowledge how much suffering his actions caused that day, with the intent of leaving him to wallow in his self-hatred "until [his] insides rot," before attacking him.
The battle quickly ends after Stranger begins strangling Sunny, threatening to keep him "down here" with him forever. Sunny is transported to Red Space in the aftermath, where he seeks Omori's protection, completely overwhelmed with his guilt and self-hatred. As they presumably merge, Stranger laments Sunny's choice, wondering if he can "really call this living," before telling him to leave him behind; "There's no hope left for me."
With Stranger pacified, a Red Hand returns Omori to the Church Of Something, where Basil asks Omori to escort him up to Neighbor's Bedroom. There, Omori 'resets' Headspace.
Stranger's battle is not intended to be won - it is instead essentially a cutscene that will end on the sixth turn. His behavior in the battle is completely scripted and he will never deviate from it:
|For the first five turns, Stranger will monologue, voicing his bitterness over Sunny abandoning him.|
On the sixth turn, he will strangle Sunny, ending the battle.
Strangle: [b.hp - 1], drain 100% of target's Juice. Ends the battle.
* Stranger strangles [target].
* Stranger: Sunny... All those times that I reached out to you... Why didn't you answer? * Stranger: You promised me that we'd face this together... but you left me all alone. * Stranger: If we can't face it together... at least we can be together here. * Stranger: Sunny... I'll trap you down here with me forever.