Lucian is a marksman champion in League of Legends, the MOBA released by Riot Games in 2009, and the phrase Save The Lucian comes from players calling out urgent rescues during matches. Short callouts like this spread through gameplay clips, streams and montages because they sum up a whole team fight in under a second. It is still used as a reaction for any desperate save, especially when a support risks everything to keep the damage dealer alive.