- Not strictly Slayers related. Lina Inverse, Naga the serpent, and Gourry Gabrieve made a guest appearance for a limited time in January of 2016.
During the event plays could play a set of story related battles with either Lina or Naga. At the start of the game you could choose to have either one in your party. Gourry cannot join your party, and is more like a background NPC.
If you competed during the event period you could keep Lina and Naga in your party after the event ended, but if you didn't the option to get them is no longer available.