Short summary: She does not participate directly, but it is mentioned as one of the 7 deadly sins (protagonists of the series). Only images of Diane appear in the Opening (which was placed at the end of the episode).
Short summary: She appears for the first time. She was hiding in a dark forest all the time and using (under threat) some illusionist monsters to ward off any traveler or visitor. However, Meliodas manages to defeat these monsters and take her with Diane. She is happy to see her captain Meliodas again (she is in love), but she becomes jealous of thinking that Princess Elizabeth wants to have some love relationship with Meliodas. Then a Sacred Knight appears and paralyzes Diane, but then she is easily released. Finally, Meliodas and the Sacred Knight face and Diane does not intervene at the request of Meliodas.
Short summary: After the fight between Meliodas and the Sacred Knight, Meliodas "humiliates" the latter being almost invincible before the wounds. Diane takes him with her hand and throws him away. Then the protagonists travel to the nearest town for a doctor to cure Meliodas. While waiting for him to be cured, Diane confesses why she is in love with Meliodas and does not like her large size. Suddenly a huge mass of insects attack the city and Diane, although afraid of them, faces them for defending Meliodas. Then, in revenge, she decides to go alone to the fortress of the Sacred Knights to counterattack.