That’s what Matsuzaka Satou sought for her and for Koube Shio: a world without bitterness or pain; i.e. a world quite the opposite of the one they’d inhabited to that point. Their love for, acceptance of and devotion to one another is the fuel that keeps them moving toward that goal—that, and Auntie’s trash bag full of cash.
All that’s left is to go to the airport, let Auntie do her work, be rid of the old sad bitter world forever, and when they step off the airplane they’ll be in a happy sugar world, where they’ll never have to suffer or despair again, and where they’ll have each other.
That was the plan, at least. Ironically, it’s Satou’s love that makes her take off her ring, so it won’t be sullied by the work of dressing Shouko’s corpse (if she is, in fact, 100% dead when we see her). Forgetting that ring, that symbol of their love, and going back for it at the worst possible time, proves to be Satou’s undoing.
Auntie ties Taiyou up in between “abusing” him—rape is heavily implied)—she didn’t gag him, perhaps because she liked hearing him squeal. That preference is also her undoing (if she cared about self-preservation, of course), as he’s able to get a call to Asahi telling him where he is.
Asahi arrives just as Taiyou escapes—and happens to bump into Satou and Shio in the lobby. They should never have come back for a stupid ring.
Satou and Shio head upstairs to find Taiyou, but they get away from him as well (he’s tied up) as Auntie, who assumes Satou is well on her way to freedom (and damn well should be) ignites the fire on the twelfth floor that will engulf Shouko and supposedly, any evidence tying her to Satou.
Asahi hurries to Room 1205 and finds Shouko there, dead and surrounded by flames, inflaming his rage even more. When he, Satou and Shio cross paths again, he lets her have it with his bat, injuring her leg, but Shio steps between them to prevent further violence.
Shio, exercising her own agency, tells her brother she’s done with her family, and all she wants or needs is Satou, and he’s just going to have to deal. Asahi tells her that their mother only abandoned her because she was in over her head and didn’t want to become their monster father (whom she poisoned to death).
But it doesn’t really matter why she did it anymore; Shio has moved on and isn’t coming back. She’s going to live for herself now, as Asahi should learn to do, rather than defining his life as finding and protecting her. Just then, the flames cut their chat short, and Satou and Shio make a run for the roof…where they are trapped.
Shio tells Satou that it would be alright if they die together by jumping, because they’ll surely be reborn together in that new world they’ve been hoping to reach (but again, couldn’t thanks to one dumb ring).
That potential New Happy Sugar Life flashes before them as they fall, but Satou makes one small change to Shio’s plan: she doesn’t let Shio die, shielding her from the impact of the ground with her larger body.
Shio survives, but Satou does not. She and Shouko are mentioned in the same news report, but as casualties of the fire, not murderer and victim.
Rather, Auntie is suspected, and gladly surrenders herself, having done everything she could for the sake of her niece’s love. Satou’s teacher is arrested in front of his family, Taiyou continues to obsess over his angel in his room.
As for Shio, she’s in hospital, and Asahi comes to visit her, promising to fill the void left by their parents, by society, and finally, by the loss of Satou. But Shio smiles in a very Satou-esque way; there is no void, not from her perspective.
Shio believes Satou sacrificed herself and became a part of her—which is kind of true, in an emotional sense—and as such Shio feels she’ll never be alone again. She still doesn’t need Asahi. She gained more than she lost, and she’s resolved to live her best life for herself and Satou. How exactly she’ll be supporting herself, a minor with no money or job, is left unspecified.
HSL is the story of deeply damaged people and the different ways the consequences of that damage unfold in their lives. There’s a solid causality to everything that, while hardly absolving most anyone of their numerous crimes or obsessions, at least explains them satisfactorily, and makes them subjects of pity rather than simple loathing.
People can grow up to be decent people even if there’s abuse or trauma in their lives, and without traditional families, or no families at all. But that’s an ideal; it doesn’t always happen. It usually doesn’t happen. And when it does (see Taiyou) it doesn’t always mean someone will “turn out” “alright.”
But even in the darkest places, some small amount of light can emerge, some small amount of happiness can be found, and a sweet but twisted love can take root between kindred damaged souls, filling their jars and giving them reason to keep living.