A 55-year-old doctor suddenly finds himself reincarnated as an adorable 5-year-old prince!? Lirias, the youngest prince of the Arsaheim Empire, regains his past-life memories after falling into a lake. In his previous life, he was a dedicated doctor who saved countless lives. Now, in this new world, he receives the blessing of Lu, a revered Spirit of Light. But what challenges await him as a royal child with medical knowledge beyond this era? A heartwarming reincarnation fantasy begins!