(himawari), which typically symbolizes loyalty and brightness, to contrast with the "night" (yoru), representing the dark and secretive nature of the plot. YuruYuri Wiki
For the genuinely curious (and of legal age), the works associated with this phrase are available through various channels: himawari wa yoru ni saku
Within adult anime forums and tracking sites like The Movie Database (TMDB) and IMDb , Himawari wa Yoru ni Saku is frequently praised for its technical merits. Technical Profile & Reception which typically symbolizes loyalty and brightness
The flower represents the individual—specifically, the identity that is defined by external validation (the sun). to contrast with the "night" (yoru)