Lotta

Lotta is the younger sister of Einar. She, Einar, and their mother lived a peaceful and simple life in northern England before Viking raiders invaded her village. She was later killed while trying to attack one raider in front of Einar.

Trivia
Lotta is an anime-original character. She is likely the young girl shown being taken away by warriors in Einar's flashback in Chapter 57 (p. 14), but she is not named.