Assassin has been created by the cooperation between the secret agents of Saint Foundation who were carrying out their missions while disguising themselves among the students. These agents have been working even before the phenomenon that struck this world had isolated the 3 schools which were founded by Saint Foundation. Dr. TK the founder of Saint Foundation who were leading these agents had gone missing and they have hid themselves from the world and the students in guilt. However, they suddenly ended their hidden lives to save the students from the invaders of Another World, the Partisans of Daramai. Existing clubs were no match for the mighty Daramai Partisans and the students cried for the help of secret agents. Therefore, Ryuin and Sia came out from the dark and established the Assassin Club and started to train the students.

Ryuin

A core character called Ryuin, AKA "the Undertaker" is famous for his harsh training session among the students. In order to stand against and win over the Partisans of Daramai, he believes hard training is inevitable. Also, he thinks the collaboration is the first thing among other things.

Sia

Sia is the last successor alive of the Fuma Clan that is known to have disappeared in the medieval Japan. After the struck of phenomenon, she has secretly been helping the students with her ability alone and then later joined forces with Ryuin and his companions and actively participated in establishing the Assassin club.