Seiichi and Saria train under Artoria to become adventurers. During their training the three of them are teleported into a dungeon by a demon’s trap.

The dungeon they find themselves in the stronghold of the Black Dragon God, the strongest member of the Demon Lord’s Army. Artoria gets separated from Seiichi and Saria in the dungeon and the giant Black Dragon God appears before her. Then that overwhelming threat attacks! Can Seiichi and Saria save her in time?!
I'm so happy I got to be Seiichi's wife!
!أنا مسرورةٌ جدّاً لأنّي أصبحت زوجة سيتشي
Ich bin so froh, deine Braut werden zu können!
¡Soy tan feliz
de ser tu esposa, Seiichi!
¡Qué feliz soy
de ser tu esposa, Seiichi!
Je suis tellement heureuse
d’être ton épouse, Seiichi !
Sono tanto felice di essere diventata
la moglie di Seiichi!
Eu sou tão feliz de ser a esposa do Seiichi!
Я так счастлива, что стала женой Сэити!