After Meliodas learned that Sennett, Dana's daughter, is imprisoned in Baste Dungeon, he, together with Elizabeth and Hawk, headed there in order to save her. On their way to the dungeon, they encountered the wandering Diane who was confused and didn't remember what she was doing.
Diane, who had fallen for the Holy KnightRuin's illusion, thinking her captain was Ruin, attacks him. Looking at her eyes, the young man immediately understands that she couldn't see them. As the three flee in order to avoid a battle, they find shepherds and hide them along with themselves, since the civilians would have been caught up in the fight. As they hide, however, Meliodas falls for Ruin's illusion as well, and he, thinking Diane was Ruin, immediately attacks her by slashing from above, and then deflects the sharp pillars Diane sends toward him.
Later, Diane is seen trying to stomp Meliodas with multiple hits, only for him to dodge all the attacks. When she compliments him for being strong even though he was a "midget" Holy Knight, he also compliments her for being fast though she was a giant Holy Knight. As their battle continues, Elizabeth desperately screams for them to stop, causing Diane to temporarily regain her senses and recognize a young shepherd, whom she had met on her way to the Baste Dungeon. However, she is immediately hypnotized again, and starts attacking Meliodas, once again thinking he was Ruin.
After Elizabeth removes Ruin's staff's bell, the object that allowed him to hypnotize Meliodas and Diane, he loses his hypnotizing abilities, resulting in both of them to regain their sense and stop fighting. The former then stops Ruin from killing Elizabeth and then defeats him.