Complex sentence: Their mission is to save Fiel's sister, Dorothy, who was kidnapped by monsters.Dorothy's cat, Toto, has the ability to transform into a Lex and becomes the source of Fiel's Katena powers.
Split into simpler sentences: Their mission is to save Fiel's sister, Dorothy, who was kidnapped by monsters. Fiel and Dorothy's cat, Toto, has the ability to transform into a Lex and becomes the source of Fiel's Katena powers.