Diane is the Serpent's Sin of Envy of the Seven Deadly Sins. She is a member of the Giant Clan and is thus much larger than ordinary people, including her fellow Deadly Sins. Her Sacred Treasure is the War Hammer Gideon, which she uses in conjunction with her inherent power, Creation. During the New Holy War arc, Diane's strength was fully acknowledged by the former King of the Giant Clan, Drole as he himself died protecting her after declaring her as his successor, making her the next potential ruler of the Giants as well as the unofficial "Giant Queen." She is also currently the wife to King, who is the current King of the Fairy Clan. As a giant, Diane is several times larger than an ordinary human being. She is a fair maiden, described as "lovely, beautiful" with purple eyes and medium length brown hair which is tied up into large twin tails. She has a well-endowed and curvaceous body. Similar to most of the other Seven Deadly Sins, her facial appearance is relatively childlike and has shown little change over the years. Diane's wanted poster depicts her with light-colored hair. Her symbol, which is of the Serpent, is located on her left outer thigh. When she was still a child, Diane wore ragged clothing until King made her a new set. Her clothes during the earlier part of the series resemble what King made for her, having sewn it herself by using leather derived from Dusk Bison skin. Her earlier attire consisted of a short-sleeved one-piece orange suit, boots with five crossed laces that extend almost up to her knees, and two finger-less gauntlets of a blue-grey leathery material covered in shiny steel stud - with the right gauntlet having been destroyed by Gilthunder during the fight in the Forest of White Dreams. She also wore a backpack previously used by Meliodas. She wears a short pink sleeveless dress with white puffballs down the front while human size or the Boar Hat uniform while serving at the bar. Ten years ago, Diane —as a Holy Knight— wore a full-body orange armor with a unique helmet like the rest of her fellow Deadly Sins. After Hendrickson's defeat, Diane wears clothes made by King that are almost the same style as her previous one, except for an inverted triangle cut on the chest and the skirt. She also wears black underwear resembling bike shorts underneath the skirt. During the New Holy War, Diane wears new clothes made by Merlin. Diane is a very friendly Giantess and is also very confident regarding her abilities, appearing to generally consider Holy Knights as weak. She cares very much about her captain and holds very strong feelings for Meliodas, often cuddling him and becoming very delighted from compliments. Her feelings are strong enough for her to overcome her fears for his sake. Diane can become extremely fierce and hostile towards anyone who threatens her friends. Diane also gets jealous when Meliodas does perverted things to other girls. In Japanese, she refers to herself with "boku", a word for "I" typically spoken by young males. Due to her size, she cannot help Meliodas in any way other than fight for him. She has expressed her strong desire to be smaller, contrary to Elizabeth's desire to be strong. Despite Diane stating that she has no interest in humans, she still selflessly saves people who are in danger like when she risked her life to protect the elderly man in Vaizel and Zeal. Despite her brave and strong appearance, Diane is a somewhat emotionally fragile person as shown by her hatred of loneliness. This was portrayed when she was a child and insisted that King stays by her side when she was sick instead of getting herbs to heal her and when she waited in tears for him to return to her. Diane showed the same kind of feelings towards Elizabeth after she was kidnapped by Vivian.