1960s --- Tokyo. Shin is a boy who lived happily despite being poor, loses his mother who is his only family member, and falls into deep misfortune. Itsuki, a boy who saves Shin also lost his older sister. Those two boys are joined by Tae, a girl who can see youkai and together with Shin's guardian spirit Suu-san and new Youkai such as Nekomata, they take on a mysterious incident in order to retrieve the souls of their precious family! And what is the shocking truth that awaits them...!? An origin story for how Lord Enma became the rule of the Yomakai. (Source: Wikipedia, edited)

With summer vacation coming to an end, the girls are having as much fun as they can with their remaining time. However, their daily shenanigans are cut short when Suguru Koshigaya wins the grand prize of a lottery—tickets to Okinawa! After hasty preparations, the Asahigaoka group embarks on a three-day trip for their final summer getaway. Upon arriving in Okinawa and checking into an inn, the group comes across Aoi Niizato—the young daughter of the inn's hostess. Despite being of similar age, her mature demeanor leaves Natsumi Koshigaya reflecting upon her own childish nature. With the sign of an unexpected friendship blooming on the horizon, the girls waste no time diving into their ambitious sightseeing plans and regional activities! [Written by MAL Rewrite]

From the depths of space he is coming... Ancient beyond understanding, his power is immeasurable. He has destroyed half the universe and is on his way here. He is... Genma. Only two people are aware of the imminent catastrophe: Princess Luna, a modern day prophetess and Vega, a cybernetic crusader from a world long since ravaged by Genma. Determined to spare the Earth from a similar fate, Luna and Vega must try to mobilize the most potent psychics in the world. Together, this army of fledging psychic warriors must succeed where billions have tried... and failed. But will they be able to gather their champions in time? Genma's agents are already on Earth to ensure that their master meets with no opposition! (Source: AnimeNfo)

The story on Arcadia's mystery, on which the 13th television episode was based.