Taking place after the events of the fourth film, the series centers on 11 yr old Keisuke Amano, Natsume's younger brother (both of whom are the children of Keita Amano and Fumika Kodama of the original Youkai Watch anime) who doesn't believe in any supernatural phenomenon around him. But as he notices his sister is frequently comes back home late, he decided to stalk her, only to find out she is doing her duties exorcising evil Youkai alongside her friends Touma and Akinori, and running a Yo-Kai detective agency. With their secret revealed to him, Natsume decided to let him tag along in her activities as they investigate Youkai crimes and take on evil Youkai to maintain peace all over the city. (Source: Wiki)

Six years ago at the magic school known as the Tower of Fang, a grave accident happened involving the magical sword Baltanders and the magic user Azali. Unable to control the sword's power, Azali was transformed into the shape of a great dragon who since that day became known as Bloody August. Krilancelo, a young magician at the Tower who cared greatly for Azali found much to his disgust that the elders of the Tower of Fang were less than willing to save Azali and wanted rather to pretend the accident never happened. Angered by their stand, Krilanceloa swore that he would find a way to return Azali to her former self. Thus he forsook the name Krilancelo and declared himself Orphen, leaving the Tower and his magical studies behind to wander the world... (Source: ANN)

As World War II reaches its conclusion in 1945, Japan faces widespread destruction in the form of American bombings, devastating city after city. Hotaru no Haka, also known as Grave of the Fireflies, is the story of Seita and his sister Setsuko, two Japanese children whose lives are ravaged by the brutal war. They have lost their mother, their father, their home, and the prospect of a bright future—all tragic consequences of the war. Now orphaned and homeless, Seita and Setsuko have no choice but to drift across the countryside, beset by starvation and disease. Met with the apathy of adults along the way, they find that desperate circumstances can turn even the kindest of people cruel yet their youthful hope shines brightly in the face of unrelenting hardship, preventing the siblings from swiftly succumbing to an inevitable fate. [Written by MAL Rewrite]

If you're in a big trouble, call the World Welfare Work Association or WWWA. They will send out a team of highly trained capable agents called Trouble Consultants who can solve your problems. But if the team they send you is the Dirty Pair, there will be a lot of collateral damage aside from solving your problems. (Source: AniDB)