Rosie

Rosie's real name is Oasis, a member of the imperial knights of Skytria Empire 1,500 years ago. 1,500 years ago she was the sister of Mojave (Redisands in Korean webtoon) and was tasked in finding black magic places in Skytria. Eventually she realized the magic traces were leading to Claudia. The silversword family realized Claudia was practicing black magic and putting the empire in danger. Snolled/Dellons was unaware of this and fought against Mojave and killed him. Claudia's sister, Arial, then suddenly stabs Claudia and kills her. Oasis, furious about Mojave's death, goes and kills snolled too. The silverswords lied and accused Snolled of murdering Claudia and kept it a secret what truly happened. She becomes one of the seven knights after receiving praise for killing Claudia's 'murderer'.