Reach level 300 and get 20,000 mana. Select the "Fight strongest person in game" option in Zeta's wish system, then defeat Baal.
Easy Mana
This trick requires healing and may cost some HL. First, choose the character you want to earn Mana for and make them the leader. Then, summon all of your characters and any weapon (preferably a sword). Have the leader throttle all of the summoned characters until they are completely obliterated. Check your status to see how much your Mana has increased. Repeat this as many times as desired. Note: Do not worry about thrashing lower level characters; the higher the level, the more Mana you get for killing them.
Play as Alec
Defeat Salome and Alec in Chapter 8-6.
Play as Asagi
Reach level 1,000 and get 100,000 mana. Select the "Challenge the next protagonist" option in Zeta's wish system, then defeat Asagi.
Play as Babylon
Reach level 200 and get 9,000 mana. Select the "Fight against Babylon" option in Zeta's wish system, then defeat Babylon.
Play as Castille
Reach level 100 and get 5,000 mana. Select the "Fight with hero" option in Zeta's wish system, then defeat Castille.
Play as Cider
Reach level 160 and get 7,000 mana. Select the "Fight against Cider" option in Zeta's wish system during Chapters 3 through 8 then defeat Cider.
Play as Dark King
Reach level 120 and get 5,500 mana. Select the "Defeat Dark King" option in Zeta's wish system during Chapter 6 in your third cleared game and defeat Dark King.
Play as Etna
Reach level 80 and get 4,000 mana. Select the "See the ending" option in Zeta's wish system, then defeat Flonne, Etna, and Laharl.
Play as Flonne
Reach level 70 and get 3,000 mana. Select the "Fight ally of justice" option in Zeta's wish system, then defeat Flonne, Etna, Laharl.
Play as Pram
Kill over 60 allies before Chapter 9 and defeat Pram.
Play as Prinny
Reach level 10 and get 1,000 mana. Select the "Make a Prinny" option in Zeta's wish system, then kill a Prinny in a normal battle.
Play as Robosuit
Reach level 200 and get 30,000 mana. Select the "Want strongest robot" option in Zeta's wish system, then defeat Robosuit.
Play as Salome
Reach level 180 and get 8,000 mana. Select the "Fight with Salome" option in Zeta's wish system during Chapter 5, then defeat Salome.
Play as Valvolga
Reach level 250 and get 10,000 mana. Select the "Fight against Valvolga" option in Zeta's wish system during Chapter 1 through 8, then defeat Valvolga.
Play as Zeta
Reach level 300 and get 15,000 mana. Select the "Fight with the strongest demon in space" option in Zeta's wish system, then defeat Zeta.