Fog Mother is the main antagonist of the 1994 Kamen Rider DVD movie Kamen Rider J. She is a massive mechanical alien parasite from space who roams from planet to planet devouring their life forms to spawn her children.
Arriving on Earth, Fog Mother sent her three children Garai, Agito and Zu to find a sacrifice for her so she could use the energy to awaken their siblings and have them devour all life on the planet. Garai, Agito and Zu selected a young girl named Kana to be the sacrifice, abducting her and seemingly killing her friend, environmentalist reporter Kouji Segawa. Fog Mother then instructed Garai to prepare the ritual to sacrifice Kana.
However, Kouji was revived by the Earth Spirits and given the power to transform into Kamen Rider J to fight back against Fog Mother. Sensing J's holy energy, Fog Mother sent Agito to terminate him for good. After J killed Agito, Zu went to fight him but in the process was fatally wounded and flew with J into the Machine Beast Mothership.
With the ritual now ready, Garai fought J while Fog Mother attempted to feed Kana to her brood. J managed to kill Garai, but was trapped by Fog Mother before he could go and save Kana. However, with the holy energy of the Earth Spirits, J grows giant and saves Kana before facing off against Fog Mother in her Machine Beast Mothership form. After a destructive battle, J defeated Fog Mother with a kick to her mechanical face on the front of the war machine, causing the mothership to break down.
However, not done just yet, Fog Mother grabs onto J with her tentacles and pulls J into the mothership, where she reveals her true insectoid form to him. Fog Mother curses J for destroying her "adorable" children and attempts to avenge them by destroying J along with her. However, J manages to get free of Fog Mother's tentacles and escapes the Machine Beast Mothership before she explodes.