Humans with the ability to merge (transform) with messengers (foreigners). Those who protect people from threats from other worlds that attack this world through gates—they were called "Logicians."

This is the story of the growth and friendship of two Logicians girls, Yurine Sena and Giselle Sanders, who belong to the Kyoto branch of the ALCA (Alka) organization for countermeasures against other worlds.