The Testament form is Illya's most powerful and chaotic form. It occurs when her normal powers prove too weak to defeat an opponent, so she taps into her Holy Grail core, granting her immense power but at the cost of unhinging her personality. Despite her personality becoming wholly overshadowed by Testament's power, Illya's core motivations still remain: Her love for her family and her deep wish to protect them and Fuyuki City. Views others as obstacles or "toys".