rather than an omnipotent God, Sekai is just a scapegoat for all evil and impurity of this world. She does this by absorbing - as in getting raped by all the impurities of this world - every day to keep the world going on. MC learns of this and convinces Sekai to run away with him. They run away to an uninhabited island, to a shed, but the long journey and the 'services' Sekai has given every day takes it's toll, killing her right then and there. While MC laments everything there is, the maid shows up to the MC, revealing herself as a supervisor for the 'real God', and makes the MC remember about his and Sekai's 'fate'.
We learn that long, long ago, MC was supposed to be the actual sacrifice for the 'services' Sekai goes through every day, while Sekai was his then fiance. The day before the sacrifice, Sekai begs to God to take herself in MC's place. The God finds this amusing and readily accepts her. On the day the sacrifice should take place, God tells what happened yesterday to MC and tells him about a game he thought up. God promises to bind the two's souls together, so that they will meet again and again, reincarnation after reincarnation. God tells MC that it'll take Sekai as sacrifice every single time they're reborn and challenges him to break through this fate somehow if he wants to save his fiance. For Sekai that sacrificed her life for him, MC readily accepts the conditions, binding himself into this endless cycle.
The maid tells him that this bond between him and Sekai is the reason that he proposed to Sekai the moment he laid his eyes on her. She also tells him that this is the 10.123rd cycle once MC asks her. MC shrugs and retorts with a 'Just that much?'. The maid, as the supervisor for each and every cycle that happened, tells MC that this is a futile game that he is playing and the only way for him to win somehow is to somehow find a so called 'bug' within the game - which he could not find in the last 10 thousand cycles. The MC also mentions by the way, that for the last couple of days that they were running, Sekai had not performed any service and the world had not ended nevertheless. The maid tells him that the World will end, according to answer that he will give. The maid gives him two choices: ending, or restarting this game. Confirming that restarting the game will bring Sekai back to life - though both as their new, reincarnated selves, the MC chooses to continue this impossible game. He resolves himself that he'll do this how many times it'll take.
In the epilogue chapter, we see the MC and Sekai in a limbo of sorts, with both of them together alone. Sekai apologizes to the MC for having to go through this game for her countless times. In reverse, the MC apologizes back for having Sekai go through the torture of 'service' countless times, and blames the God for being the source of all this in the first place. Sekai laughs, and tells him that she admires him that can still point his finger against God even in this unknown limbo of space and time. She tells him that he might be the only one to break this unending fate of theirs. After a short silence, she tells him that they'll have to start all over again with their relationship and asks if he'll ask her hand in marriage again. And the MC answers back with an 'of course', and tells her that this one thing will be their one and only fate that remain unchanged, ending the series.