Maou-sama to Sunadokei - Tensei shitara Yousei-san de Shourai no Maou ni Yamareru HanashiNewMaou-sama to Sunadokei; Maō-sama to Sunadokei ~Tensei Shitara Yōsei-san de Shōrai no Maō ni Yamareru Hanashi~; The Demon King and the Hourglass; The Demon King's Hourglass - Reborn as a Fairy and Claimed by the Future Demon King; 魔王様と砂時計; 魔王様と砂時計～転生したら妖精さんで将来の魔王に病まれる話～

https://www.cmoa.jp/title/287310/\n\nLouis is a prodigy who serves as a court magician and possesses talent that surpasses even adults. Living alone with his frail younger sister, he one day captures a fairy in the forest. That fairy is actually Eleanor, a girl who reincarnated into another world as a fairy on the hero’s side in this otome game. Small enough to fit in the palm of a hand, she is forced to live inside a cage. However, by drinking Louis’s blood, she can transform into a human-sized woman… Louis pours his obsessive, unhealthy love onto Eleanor. Despite his beautiful appearance and promising future, what is this boy’s true purpose in this world?