Diane is a Giant and a member of The Seven Deadly Sins, her sin is Serpent Sin of Envy
Diane was previously a part of the Giant’s Clan but she later left due to unknown reasons. During her travels, she met a few knights who drew their swords and attacked her for being form the Giant’s Clan. Before they could attack, Meliodas quickly arrived and began attacking them. He then began to chastise them for attacking a single girl. After the knights retreated, Meliodas asked Diane if she was scared which made her feel as if she was his size. Diane later became one of the Seven Deadly Sins along with Meliodas.
She, along with the other members of the Seven Deadly Sins, was summoned by the Great Holy Knight for unknown reasons. They entered the room only to find the Great Holy Knight screwed by many weapons. The castle was then quickly surrounded by all of the Holy Knights of the kingdom. Diane was somehow able to escape the castle and ended up in the Forest of White Dreams where she forced the Prankster Imps to hide her.
Diane was created by Nakaba Suzuki as one of the main characters in the series. Her character is mainly inspired by the giants, a creature from mythology.
Since her introduction, Diane has regained her Sacred Treasure and eliminated his dislike of Elizabeth through the various trails and adventures they have shared.
Diane towers over mainly all of the characters at her height of 30ft (914cm). She has pink eyes and brown hair often in a twin tail. Diane also has a curvaceous figure and child-like face which she retains over her ten years away from the other Sins. The symbol of the Serpent is located on her left outer thigh. Diane’s main attire is a one-piece orange suit, a pair of orange boots that almost reach her knees and a fingerless gauntlet made up of a blue material and covered with studs.
While looking for ingredients alongside Elizabeth during the Bzyel fight arc, she and Elizabeth shrunk in size due to startling a King Trumpet type mushroom called the Chicken Mantango. In this state she is about Elizabeth’s size and wore Elizabeth’s clothing, a purple blouse with a black ribbon, a dark mini skirt and a black stocking on the left leg.
Diane is generally a friendly person to people who are friendly to her. She cares deeply for Meliodas and often cuddles him. However she often throws tantrums, often against Meliodas, when she is upset or envious. She is also shown to be very caring and helpful when innocent people are in danger. Diane is also shown to be afraid of bugs.
Meliodas, Elizabeth and Hawk stumble on a sleeping Diane after chasing the Prankster Imps. Diane quickly grabs Meliodas and holds him up in the air thinking he is a Holy Knight. After hearing Elizabeth call his name and looking at him, she begins to cuddle him. She quickly learns that Elizabeth is travelling with Meliodas and throws him into the ground and continuously punches him for “cheating” on her. She calms down after Meliodas explains the situation and she apologizes. Meliodas then questions Diane about what happened ten years ago because he has almost no memory of that day. Diane then decides to join Meliodas to help him find the other members of the Seven Deadly Sins.
A giant thunder cloud then loams over the area and a lightning bolt descends ensnaring both Diane and Meliodas. Holy King Gilthunder then appears to capture them. Gilthunder reveals the reasons for wanting to capture the Sins, for avenging his father the late Great Holy Knight Zarthas and proving he has surpassed his father by beating the ones who are said to have killed him. However, both Diane and Meliodas break out of the lightning simultaneously and Meliodas begins to approach Gilthunder telling Diane not to interfere. She then quietly observes the battle between them.
After Meliodas gets the information he needed about the location of two other Sins, he tries to leave with everyone else but Gilthunder refuses to let them escape. Diane then picks him up and throws him away causing her right gauntlet to fall apart due to his escape attempt. After returning to the Boar Hut, they begin to move towards Baste Dungeon to rescue the Fox Sin Ban.
Diane, and her team travel to Dalmary first, a town near Baste to have Meliodas see Doctor Dana for his serious injuries. Diane decides to enter the dungeon alone to retrieve Ban, telling Elizabeth to stay with Meliodas. Elizabeth argues with Diane, saying that she wanted to be of help. But they are suddenly interrupted by Hawk who draws their attention to a swarm of giant insects coming their way.
Despite Diane's great fear of insects, she soon pulls herself together and annihilates the swarm in rapid fashion. Diane then rushes off to Baste Dungeon. Despite assassination attempts on his life, Meliodas, Elizabeth and Hawk soon join Diane. When her performance against the swarm of insects is brought up, Diane finds that she doesn't recall ever killing them. While trying to remember, she notices Meliodas and Elizabeth had vanished. This was due to an illusion cast by Holy Knight Ruin who then revealed himself. Diane attacks him, but this too was an illusion and while she believed she was fighting against Ruin, she was in fact attacking Meliodas. A confused Meliodas tries to escape Diane with flees along with Elizabeth and Hawk, but soon after he unknowingly falls under Ruin's hypnosis as well. And when Diane catches up to them, Meliodas saw Ruin in Diane's place and also began attacking her. A brutal battle ensues, neither getting the better of the other. This would likely have continued until death or incapacitation, but Elizabeth discovered the source of Ruin's illusions and tricked him into letting her take the device, but not without getting mercilessly beaten.
Shortly after, Diane and the group discover the location of Ban by threatening a Holy Knight with Freisia's crushed body into telling them. When they arrive at Baste Dungeon though, Ban had already released himself from his Cell and he and long time friend Meliodas exchange "brotherly fists of love", destroying the entire Dungeon in the process. The group, now with Ban go back to Dalmaty where Diane takes care of Elizabeth until she got better.
Diane and her comrades leave Dalmaty to continue on their quest to bring all of the 7 Deadly Sins together again. find the other Sins. They encounter two Holy Knights on the way, but they are abruptly killed by a Black Hound, which Meliodas frightens away. They later arrive at the Capital of the dead where they had been informed that they could find information on King, the Deadly Sin of Sloth. They set up the Boar Hat there with Diane as the waiter and Ban supposed to be the cook, but the latter left while nobody was looking. They decide to look for Ban, but they come across Ban in the midst of battle. Diane quickly recognizes the foe. It was actually King. Upon seeing Diane, King left the scene.
Back at the Boar Hat, they get info about how to Enter the Capital of the Dead by two young siblings visiting their restaurant. They manage to enter into the Capital of the Dead but are quickly met by Holy Knight Guila. She antagonizes the group, forcing Diane to protect the others with her body. They were on the brink of defeat when King arrived and defeated Guila with the utmost ease. The reason he did not join them before was due to past history with Ban and a serious misunderstanding. But that had mostly been resolved in his battle with Ban. They then return to the world of the living, where they find Guila's near death body, as nearly killing one's self is a way to enter the Capital of the Dead. Rather than killing her, Meliodas merely played a prank and wrote on her face while she was unconscious. Later, King remarks about their weak performance compared to his own and it is revealed that Diane, Meliodas and Ban had all lost their sacred treasure weapons for one reason or another, much to King's shock, as sacred treasures amplify the power of the 7 Deadly Sins greatly.
Immense Strength - Diane has tremendous physical power. simple punches or stomps from her can create craters and chasms. She was able to throw Ban, Meliodas and Gowther together, a distance of over 40 miles. It was hinted to be at faster than the speed of sound too as Gowther said he could not hear the sound of their voices despite being right on top of Ban.
Gideon - Diane's sacred treasure. It is a massive war hammer, roughly Diane's own height and it weighs 1.1 tons. With this weapon, Diane's already fearsome blows are amplified to immense levels to the point of upchucking a mountain sized chunk of earth and leveling a huge area, propelling large boulders into the sky.
Creation - This is an ability exclusive to the race of Giants. It allows Diane to rapidly manipulate the earth, including for offensive purposes such as creating giant pillars of earth to crash into the unfortunate foe.
Diane rapidly converts the minerals of the Earth into sand. It acted like quick sand when used against Holy Knight Guila.
Diane transforms her body into metal, increasing her mass and hence her raw power.
Used in conjunction with her Sacred Treasure Gideon. A single strike with Gideon destroyed the entire town of Byzel. The flying debree is highly dangerous but if one were to somehow survive the shockwave and the debris, so much earth that a mountain sized chunk is unearthed large.
Diane Slams Gideon on the Ground and forms a huge spike of earth so large that it dwarfed the structures in Liones and could be seen even away from the City. It vaguely resembles a giant blade.
Diane levitates several rocks and stones and hurls them towards the enemy.
Diane forms a pillar of earth underneath the enemy, then it shoots up at such speed that the opponent cannot remove their person until it is over.
Diane creates 2 giant iron fists by spinning Gideon overhead. With another gesture, both fists slam into the intended target.