Whether one's preference is the manga or anime, one thing can be agreed on by many fans of Erased -- seeing Kayo Hinazuki married with a child after Satoru Fujinuma wakes up from his 15 year coma is gut-wrenching, and not in a good way. Satoru's struggle to save Kayo's life bound the two together in a way that seemed they could become the childhood sweethearts who actually earn a happily ever after, linked by a pair of mittens and Satoru's desire not only to save Kayo from her murderer, but her abusive household as well.
However, hard as that initial gut-wrench may be, to blame Kayo for her decisions not only flies in the face of Satoru's sacrifice, it's layered with old sexist stereotypes.
Though the story of Erased is told through Satoru's eyes, Kayo's decisions can only be understood through her own interpretation. Throughout the events, Satoru has the memories of being 29, giving him a huge advantage over her even if his state of mind doesn't remain mature. Kayo, however, has only ever been in elementary school.
To her, Satoru is the center of the plan that gets her out of her mother's grasp, and while she might have been frightened by someone invading the sanctuary of the abandoned school bus, she never saw it as the threat that Satoru did. In fact, the main purpose of it all was fulfilled when Kayo's grandmother came to take her away to a better home. She couldn't possibly understand what he was truly protecting her from. For both of them, as children, any ideas of romance were pure, but juvenile. Though the two might hold hands, that is hardly an obligation.
Kayo's later decision to marry Hiromi Sugita was, in fact, the most she could do to honor Satoru's sacrifice, whether she knew it or not. Hiromi would have been another victim of the serial killer had Satoru not caught Gaku Yashiro's attention, making their marriage and their baby entirely due to Satoru, and -- in the Erased anime adaptation -- it's the sight of a happy and smiling Kayo with her baby that helps Satoru regain his memories after waking from his coma.
Even if Kayo had spent 15 years pining after her elementary school crush, waiting and waiting for the slim chance he might wake, she may not have been able to help Satoru regain his memories as a miserable husk of a woman who had squandered the life he once saved only to cry over him. The best thing she could do was live and be happy in order to honor Satoru and how he saved her -- in more ways than one.
Expecting Kayo to wait for Satoru also enforces incredibly sexist expectations for women. Women are meant to be rewards for the heroes at the end of a journey. The idea of the guy 'getting the girl' is unfortunately common in media, not only turning the girl into a material possession the man can now own, but making him a worse character for it. If a man is heroic, then his reward ought to be the people who were saved by those heroics instead of a pretty girl. Satoru's reward for outwitting Yashiro is the knowledge that there are people out there, including his own mother, who wouldn't be there without his actions.
If he expected Kayo to fall into his arms just because they held hands a couple of times, that would seem like supreme entitlement. If she fell into his arms of her choice after having spent 15 years waiting for him to wake up, that would make her unhealthily dependent but also very different from the resilient young girl she had once been. So by making Kayo Satoru's 'reward,' not only would it ruin their characters and relationship by default, it would fall into old sexist ideals of dashing heroes and pretty girls that already ruins so many fictional bonds.
While the initial realization that Kayo and Satoru were never meant to be can be disappointing, in the end, it's best for both of them. Kayo should not be expected to wait around for a childhood crush to maybe never wake up, and Satoru wouldn't want her to waste her life like that. Instead, she and Hiromi were able to marry and have a baby who never would have existed without Satoru, a sight in the Erased anime that brings all his memories crashing down at once. He saved her life and she lived it to the fullest, both honoring each other the best way they knew how. So while Kayo and Satoru may never be a romantic couple, they will always be linked by a pair of mittens.
