The smaller red dwarfs fuse throughout nearly their entire body. While in many stars only the core or a shell around the core is actively fusing its hydrogen supply, these skinflint stars can process nearly all of what is available to them. This begets their absurdly long lifespans (for the heaviest about half a trillion years)- and has fascinating consequences at the end. Such tiny stars balloon only modestly when the end comes- they betray the near-depletion of their fuel in other ways. The luminosity increase instead comes from a rise in the star's surface temperature, shifting the star's color towards blue- though at best this only reaches the heights of color that mint stars can achieve. For the smaller stars, this stage lasts for a time similar to that of the lifespan of orange and yellow stars- pushing worlds that previously were frozen into the habitable zone.
