To get the character's Ra-Seru spell, go to the Genesis Tree in which the character first got their Ra-Seru; but you must do it after Songi is defeated in the Seru-kai or it will not work. Here is where each character must go

Vahn: Sol Tower's Basement Genesis Tree (Since Rim Elm is destroyed)
Noa: Mt. Rikumoa
Gala: East Voz Forest

To get the Juggernaut Spell, go to Ratayu after defeating Songi in the Seru-kai. Then, go to Van Saryu, get the Evil Seru Key, and use it to get into the basement of Ratayu, (where Van Saryu was fought). At the end of the corridor is a chest that contains the Evil Talisman. Equip it to get the Juggernaut spell. The Talisman also gives Encounter Rate Decrease.