Lagoon Engine (ラグーンエンジン) is a manga by Yukiru Sugisaki. It has been suggested that this series is a sort of prequel to the manga series Lagoon Engine Einsatz, but no statement has been made by the author or publishers to support this idea.
Lagoon Engine revolves around two characters: 12-year-old Yen, and 11-year-old Jin. While Yen's intelligent, calm, and thinks tactically, Jin's hotheaded and rushes into battle.
The Ragun family is dedicated to defeating ghosts, evil spirits, etc. - known as 'Maga' Yen and Jin just happen to the successors of the family, and they have to fight Maga too. In short: Yen and Jin are Gakushi.
Both Yen and Jin have Maga - though not evil maga. Yen's Maga is called Koga, while Jin's maga is named Sora. Koga is good with gathering information, analyzing and remembering things, though he's extremely bad at attacking. Sora has no intellectual power whatsoever, but his attack power is very high.
-  (Forums discussion)