I would call it a unique ending, as the turnout is almost completely different. Getting the fourth ending requires significantly altered endeavors. Two of the characters, King and Toroko, who die in the other three endings are alive at the fourth ending, and the fates of the children Curly raises are uncertain but assumed dead in the other three endings, but in the fourth ending they're revealed to be alive. Additionally, in this ending, Quote and Curly go home with the Sakamotos as opposed to the third ending in which Quote and Curly go somewhere with Balrog. Furthermore, there are two additional credit art illustrations as well as an extra credit scene, so I'd consider it a unique ending. Even then, the third ending could be considered an extension of the second ending.
I understand that.
Also, thanks for the descriptive criticism,
I find it very helpful.
Oh, also, Your mod isn't realy a fourth ending, it's just
an extension of the third one.