WARNING: The following contains spoilers for Episode 42 of Healin' Good Pretty Cure, "The King Evolved! Undermined City," now streaming on Crunchyroll.
As of Episode 42, Healin' Good Pretty Cure has truly entered its endgame, with just Shindoi-Ne and Neo King Byo-gen left to purify and defeat, saving the Earth -- and yet, it may just come at the cost of their Cure Earth. Despite the girls' best efforts, Neo King Byo-gen, having absorbed both Guiwaru and Daruizen, is no pushover, and he undermines the entire city of Sukoyaka within moments of evolving. Everything the girls care about is hurting -- their family, friends, the elements they've worked so hard all series to save... all feel the force of Neo King Byo-gen's power.
Even Queen Teateine's unexpected arrival with the rest of the recuperated Healing Animals is of little comfort. While they do manage to create a shield that prevents the undermining from spreading to the rest of the planet, even immobilizing Neo King Byo-gen in the process, it's clear that the fate of the Earth is in the hands of the Cures -- if only they can think of a way to defeat him. Asumi's plan to absorb the power of the Byo-gens is risky, but the only one that might work.
Before Queen Teateine's arrival, the Cures discovered that none of their elements could get past Neo King Byo-gen's energy barrier, even when using as many as they could at once. Thus, Asumi reasons that, since the Byo-gens grow and evolve by absorbing the power of other Byo-gens, if they used Byo-gen energy against him with the power of the elements, the Byo-gen power would allow them to bypass his shields entirely.
At which point, some viewers shoot Nodoka an awkward glance -- if she had accepted Daruizen's plea to harbor him a few episodes ago, it would have not only prevented King Byo-gen's evolution to Neo King Byo-gen, but the Cures would've also had access to the very power they now need to defeat him! But there are a few good reasons why the writers may not have chosen to go this direction.
Since Daruizen was unpurified, it was likely that he would have seriously harmed Nodoka, regardless of whether he meant to or not, and doing so would have also robbed Nodoka of an all-too-realistic internal conflict. But, given that Daruizen's plight is currently something that only Nodoka and Rabirin fully understand, Asumi isn't suggesting that they turn back time -- rather, she is volunteering.
As the only non-human Cure, having been brought into existence by the Earth itself, Asumi believes she'll be the least susceptible to the Byo-gen's powers, and the only one who can actively absorb that power into herself and use it for good. While Nodoka pleads for her not to do it, citing her own experience with Daruizen, Asumi is firm. It's her choice to make the sacrifice if it needs to be made -- and she's come to love the city and planet, not because she was made to protect it, but because of the experiences and relationships she's made. And she's ready to lay down her life if that means protecting it.
Just as they finish their discussion, Shindoi-ne tracks the girls down, leading to their final showdown. Like Daruizen before her, Shindoi-ne powers up for this final battle, evolving one last time -- but the girls' Healing Arrow reverts her to her original form. Rate is able to direct them to use Healing Oasis, a weaker attack, yes, but still powerful enough to fully purify Shindoi-ne, allowing Cure Earth to absorb the leftover Nano Byo-gen. She notes it feels weird, but she can still move, and the girls end the episode ready to go save the world.
While it's likely that this incredibly risky plan will work, it leaves Asumi's fate up in the air for the next episode, and it seems highly likely that the girls will need to say "good-bye" to their friend as abruptly as they said "hello" when she first appeared. Asumi could return to the Earth, fading out of existence, somehow be corrupted by Shindoi-ne's Nano Byo-gen or even become a regular human and lose her connection to the wind element. Or, what happens could be something completely different, but regardless, Episode 42 of Healin' Good Pretty Cure has made it clear: if the world is saved and Cure Earth has to disappear to do it -- that's fine by her.