As a devil familiar, Walgner appears as a small, dark-colored figure with horns, wings, and a tail.
After Nacht Faust interrupts a captains meeting, he summons four masked beasts to stop the captains from attacking him, with Walgner holding back Charlotte Roselei. After Julius Novachrono vouches for Nacht, the captains relax and the beasts disappear.
When Asta defeats Liebe and insists on forming a contract of equals with the devil, Walgner appears alongside Gimodelo and the other devils. The devils cling to Nacht's head and shoulders as Nacht enters the circle and compliments Asta's choice. Walgner and the other devils disappear when Gimodelo merges with Nacht to continue Asta and Liebe's training.
After Nacht admits defeat, he leaves behind Gimodelo to continue Asta and Liebe's training since their union needs more work. The devil is terrified of the possibly lethal attack again, and Nacht's other devils comfort Gimodelo.
During the invasion of the Spade Kingdom, Nacht sends Walgner to accompany Ralph Niaflem for a meeting with the Resistance in the castle town. After the first gate opens, Walgner returns to Nacht, so they merge and use Walgner's characteristic, Crow, to paralyze Nahamah and Lilith in order to drag them to another part of the castle. Nacht then merges with Plumede and traps the devils in Dark Prison Hunting Ground. The devils eventually pierce Nacht with several needles of burning ice. Nacht decides to surpass his limits and assimilates both Walgner and Plumede. With the increased magic power, Nacht creates Monument of Atonement, trapping and sealing away himself, Nahamah, and Lilith. However, the devils break out of the seal, and Walgner's and Plumede's broken masks lie in pools of shadow.
- Crow 「鳴声 Nakigoe, Viz: "Cry"」: When Walgner assimilates with Nacht via Unite Mode: Gallus, Nacht can issue a loud rooster crow that momentarily paralyzes those who hear it.
|Lucifero • Beelzebub • Megicula • Lilith • Nahamah • Lucifugus|
|Gimodelo • Slotos • Plumede • Walgner|
|Asta • Nacht Faust|
|Dante Zogratis • Vanica Zogratis • Zenon Zogratis|
|Asta • Charmy Pappitson • Finral Roulacase • Gauche Adlai • Gordon Agrippa • Grey • Henry Legolant • Luck Voltia • Magna Swing • Noelle Silva • Secre Swallowtail • Vanessa Enoteca • Zora Ideale|
|Gimodelo • Liebe • Plumede • Slotos • Walgner|