The Promise
The Foreshadow Variant for Ultimate Finale has finally been unveiled, offering a glimpse of the final Ultimate X-Men story. Because it is purposely vague, it can be interpreted in many different ways.
As a preface, Ultimate X-Men touches on many political and social issues, but the story is primarily about Hisako and Mei. Is it a platonic or romantic story? Take your pick. Even if there's more evidence pointing toward the latter than the former, from the book itself to Peach's comments to the inspirations behind the characters of Hisako and Mei.
Personally, I think the cover should be taken more metaphorically than literally. Mei descends into the sewers—the underworld. The background looks eerily similar to the Astral Plane. The manhole cover resembles the Ichiki sticker that Mei made for Hisako. きりさきmeans Point of No Return.
Hisako promised a reunion. Peach never specified what the reunion would entail or if it would align with what most readers wanted. I think Mei is leaving the physical world behind, along with everyone in it, to be with Hisako.
I'm torn about how I'd feel if it happened. But remember, she doesn't have much to live for except for her. She disowned her family. While the core X-Men are still around, the masked ones have fallen apart. She doesn't have a home. She is all she has.