Tantei wa Mou, Shindeiru.: The Lost Memory  

The Detective is Already Dead.: The Lost Memory, 探偵はもう、死んでいる。-the lost memory-

Four years ago, Kimihiko Kimizuka joined forces with "Siesta," a mysterious detective on a hijacked airplane. Together, they embarked on incredible journeys across the globe while battling a shadowy organization. However, their adventures came to an abrupt end when Siesta passed away. Now, in present times, Kimihiko attempts to lead a normal life as a high school student. Despite Siesta being deceased, things remain anything but ordinary for him.