Sebastian Smythe and Barry Allen are twins, and neither have gotten along since before their mother's murder. When the Warbler and New Direction's reunion is set in Central City, the two get a chance to repair their relationship. while Visiting Earth-1, Kara finds out about the reunion and has no idea what to do since Barry and the others had no idea that Kara accidentally went to earth 1 before but that was before Kara realized about the multiverse being a thing and how could she tell her old classmates about her being an alien but that she is actually from another earth. Glee belongs to Fox and The Flash & Supergirl belongs to the CW (Set in Season 4 of the Flash and season 3 of Supergirl)