Lagoon Engine

Yen and Jin are brothers in elementary school and successors in the Ragun family craft of defeating evil spirits. In this world, the battle with spirits comes down to a game of guessing your opponent's "name." Once you know the name you gain control over the fight. Both Yen and Jin have secret names only they know... and must keep them secret or risk death!

(Source: Tokyopop)

Lagoon Engine was first published by Tokyopop from May 15, 2006 to December 14, 2010. VIZ Media since took over the license, and published the series digitally from July 22, 2014 to January 20, 2015.