Tiara is Pride's younger sister and technically the original game's protagonist, though that's kind of a technicality. Throughout the series, she mostly hangs around as emotional support for the male love interests—the romance candidates from the original game—while they complain about Pride. She's basically a walking comfort character, more like a plush toy you hug than an actual active participant in the story. Even in the original game, the narrative is really just about Pride; Tiara fills the role of love interest rather than doing anything particularly meaningful.
Things shift once Pride gets reincarnated into the game world and takes over as the real protagonist. After that, Tiara becomes pretty much the archetypal cute little sister—spacey, always lost in fairy tale books while everyone else is grinding to become stronger and support Pride's mission to improve the kingdom. She's sweet and adds some lighthearted moments, but if you cut her from the anime entirely, the plot would carry on just fine. The story doesn't really need her there.
Content compiled by AnimeList.moe from publicly available sources.
