TL;DR to start, it's Biollante.

If you remember the original plot of Godzilla vs Biollante then you know how this fits. Rather than the creation of a human-rose hybrid that gets mixed with Godzilla's cells, it could be (hurts to say cause our boy has faced enough in his life) that Noriko is infected with Godzilla radiation and her body has absorbed it in a way that will biologically change her. Despite her bandages, she seemed to be in pretty damn good physical condition after taking full on radiation. It would make sense that America (assuming this is the path taken) would look to experiment on Noriko (assuming she is some sort of lone survivor to that heat ray) to find how she survived and to somehow weaponize her biologically.

This would fit with the tone of G-1 and add another layer to the occupation of the US and how that affected Japan. It would also continue the agony of Shikishima after overcoming his biggest hurdle only to run into one that completely ruins him after overcoming many of his demons. Noriko being his connection to finding himself again only to be lost entirely and in the worst way possible. It is devastating, but Shikishima as we have seen is the most determined man alive who must John Cena his way through everything and even though the end will have scars, he needs to be there for Akiko and those close to him.

The Biollante path is one of mass tragedy and it pits Godzilla against a foe that it can win and lose to at the same time. It can give Shikishima the horrible role of ending Biollante but by doing so ending Godzilla at the same time. He must end the story sacrificing that which is most dear to him. You initially think that its his comrades he felt he let down, his wounded soul for failing, but really its the woman he grew to love who showed him that he CAN end his war and his torment. The final song of getting past his demons is having to destroy that which he loves in order to destroy that which he hates.