Kaijuu Yon-gou was an Identified Kaiju. After its death, it was turned into Numbers Weapon #4, formerly used by Hikari Shinomiya and currently used by Kikoru Shinomiya.

Even as a Numbers Weapon, Kaijuu Yon-gou seems to vividly remember its past user Hikari Shinomiya, since her ghost is clearly visible to its current user Kikoru Shinomiya. The Kaiju also seems to be very observational and judgemental with Kikoru.