https://image.itmedia.co.jp/l/im/nl/...atplanet33.jpg
I found this entire comic sequence from one of the Japanese TF twitters that linked this comic. It's entirely in Japanese but it appears to be about a couple who finds themselves in a devastated planet (Not sure if it's Earth or not) and the woman finds herself slowly turning into a semi-anthro cat in the course of a few days (In a couple pages for us though). Once she became one the couple is confronted with another cat person who explains what's going on but I can't understand it.
-speculation-
It seems like there's a deadly disease but it somehow changed those who aren't affected by it into semi-anthro cats (I'm just saying that their heads is more cat than anthro) I guess, but those that don't turn into them are doomed to die or something like that, which is why the guy doesn't change. So rather than going with the other cat person she chooses to stay with her apparently doomed still human boyfriend. Though it seems like in the end that she may have figured that her boyfriend may be just immune and probably won't die after all and now they're both happy that they may be staying with each other much longer than they thought.
-speculation-
But that's what I think is what happened at the end, since it would explain why they suddenly became happy in the end.