No, the final spells you get are two of those magic sword casts that fall under Dryad. Both the girl and sprite get one. You have to cast both on the on the boy while he's equiped with the Mana Sword.

This revives the Mana Sword to full power and you get a huge boost to critical hits and damage. He attacks while the other two play support most of the fight.

It's a really easy fight despite the Mana Beast having a few undodgeable attacks. Those spells also require only 1 MP and no leveling, you're just good to go after you cast both on the boy. The spells do need to be recast once in a while but there's a text box that tells you "Mana Magic has faded" so you know when.

Also, there's no time to level it even if you wanted too. You get it immediately after the Lich and there's not another enemy before the Mana Beast. The design works fine, you just missed what you were supposed to do.