Mysti is a cat, cats like napping in the sun. Mysti is therefore sunbathing. Logic!
Mystic was last seen proposing to Vixa (http://daffydwagstaff.deviantart.com/art/KeenFans-Engage-513813844/not uploaded to FA) presumably after they'd done a spot of monster hunting (http://daffydwagstaff.deviantart.com/art/Mystic-and-Vixa-Monster-Hunters-273798918/http://www.furaffinity.net/view/7028794/)
Incidentally, Vixa maaaaay have been turned into the swimsuit Mysti is wearing.
dA link: http://daffydwagstaff.deviantart.com/art/MystiSwords-623348219
FA link: http://www.furaffinity.net/view/20640005/
FN link: https://beta.furrynetwork.com/submissions/artwork/public/1271646/
Furiffic link: https://www.furiffic.com/affie_beck_lauder/view/76208