Koishita Hito wa, Imouto no Kawari ni Shindekure to Itta.: Imouto to Kekkon Shita Kataomoi Aite ga Naze Imasara Watashi no Moto ni? to Omottara @COMIC

In place of her sister, Wisteria took on the job of becoming a guardian of a poisonous otherworld. One day, a man who resembled her first love dropped out of the sky. His name was Lloyd. To her surprise, he was the son of her first love! To win the hand of the princess, he has come to ask for Wisteria's partner, Saltis, a sentient holy sword. Having survived in the other world frozen in time, Wisteria easily defeated Lloyd and told him to go home... But despite her best efforts at persuasion, Lloyd refused to leave. "Please take me as your apprentice, until I get strong enough to defeat you!" So began a one-sided relationship between master and apprentice. Will her time, which has remained frozen for so long, begin to move again? A master-student love fantasy between a lonely former noble lady and a prodigy prince!