Lagoon Engine Series by Yukiru Sugisaki

Yen Ragun and his little brother Jin must solve clues to complete their training as Gakushi, people who take care of ghosts and evil spirits.

Kana Mikami has a major crush on Yen Ragun - but is it really Yen whom she's in love with?

Who's guarding the manor? That's the question Yen and Jin must answer when they confront the ghostly Maga that's haunting a creepy mansion! Can Jin master his special attack in time to slay the spooky specter?

Kana Mikami, a member of the Mikami family, has a major crush on Yen Ragun...but is it really Yen whom she's in love with? When Kana is given a book that is rumored to grant wishes to its owner, will she make her move on Yen--or will she get burned?

Yen and Jin take part in the test of courage at the Matsuri. All the kids are paired up, and have to make a treacherous journey up an old mountain path to a shrine they may or may not return from! As if the journey isn't dangerous enough, Maga await somewhere on the way ready to ambush! Will Yen and Jin make it through this one? They'll not only have to prove their courage, they'll have to prove they can survive!

The adventures of young ghostbusters Yen and Jin continue! Since a dangerous Maga spirit is likely to appear at their friend Ayato's school, Yen and Jin must enter its Hyakunin Isshu tournament. But in order to defeat the Maga, they'll have to beat the Hyakunin Isshu champion first!

Young ghostbusters Yen and Jin will stop at nothing to capture a dangerous spirit before it possesses the queen of competitive Hyakunin Isshu. Their best friend Ayato's life may be at stake in this risky gambit if they fail. But first, can they pass the tests of the mystical Yamiya in order to obtain the tool they need to defeat the Hyaku Isshu once and for all?