Her sister-in-law. Grayfia is usually strict with Rias but cares deeply for her as well. Rias is also shown to respect and care for Grayfia.
Her future brother-in-law. After Riser's defeat at Issei's hands to end Rias' engagement, she slowly came around to the idea of Rias loving Issei. However, in Volume 8 when she officially visited the Hyoudou Residence as Rias' Onee-Sama; she explained harshly how the Gremory Clan needed proof that their relationship was progressing. After the successful completion of the Ruins of Connection trials, along with Sirzechs, she congratulated Rias and Issei. Later in the side story "Let's go to the Onsen!", Grayfia shows just how deeply she cares for Issei as her little brother. When Issei formally informs her of his relationship with Rias, Grayfia has only one condition to allow it; Issei must call her 'Ane' in private times.
Sirzechs' wife. The two met each other during the war between the Old Satan Faction and Anti-Satan Faction where they fell in love with each other. While Grayfia loves her husband deeply, due to her serious and diligent personality, she often gets irritated by his laid back attitude despite his status as a Satan and constantly acts strictly towards him.
Grayfia loves her son dearly but is strict with him due to his status as the future head of the Gremory Clan after Rias and because of the special environment Millicas lives in.
Grayfia's younger brother. He appears to have some sort of grudge against her because he felt she abandoned her role as a Lucifuge. Grayfia has thought that Euclid has died during the Civil War between the Old Satan Faction and Anti Satan Faction and was shocked to know that he is alive and has returned as a terrorist.