Please due tell, in theory on the top left it tells you all the characters with available stages. If there is a menu that pops up it shows that it is the end of the story content as a soft ending you can/should be able to hit keep playing and you should be able to do the rest.
Each character has endless events in which they will gain weight. Once they hit that they will stage up. Again in the top left menu if you hit characters I can view the stages I unlocked but effectively when there is food it is being tracked.
