In Chapter 6, meet Robert then complete his "Plight" side quest.
Finn will meet you in Chapter 4. Complete his side-quest, "Finn's Plight".
Naturally occurs during the storyline, when Rubella joins Aurora's party.
At the start of Chapter 8, you will meet Oengus. Then, complete the "Plight" side quest.
At the start of Chapter 9, you will reach Piscean Village. An NPC will ask you to find her parents. Move straight and get inside the tower to solve a puzzle. Defeat the Boss to get the "Gen's Plight" side quest. Return to Piscean Village and speak with Gen.