After Diane returns to Megadozer, she hears of the death of her friend Dolores. Matrona then assigns them to meet with some Holy Knights from Liones to subdue some of the savage tribes. When Matrona and Diane arrive to an unknown location, they are greeted by Gannon, one of the Holy Knights. Matrona can't sense the presence of any savages tribe. Gannon tries tricking Matrona by making it seem like he could sense where they are. It was all a trick as Matrona was trapped by Gannon's Hollow Sound, who hopes this would get him a higher rank.
Even though Matrona is trapped, she easily frees herself with her Creation ability. The giantesses use their ability to defend themselves from giant darts of the holy Knights. However, there is one dart that gets through their defense. Diane wants to use Heavy Metal to defend herself, but Matrona sacrifices herself before she can do so. The dart is covered in deadly venom that can spread even through the smallest scratches. Matrona then kills Gannon with 329 other Holy Knights before becoming unconcious due to the poison's effect.
Matrona tells Diane that she trained her to fight so that she could become a strong woman considering all she knows is how to fight. Diane leaves in agony while some Holy Knights come to report of Diane's alleged act of poisoning Matrona and then murdering 330 Holy Knights, which would later be known as Diane's Sin of Envy. The Kingdom of Liones sentences her to death, but Meliodas hinders the sentence in the name of Bartra Liones so she could join the Seven Deadly Sins.
Meanwhile, Zalpa finds Matrona lying around and treats her wounds for three days straight without rest, thus saving her life without Diane knowing.