Shin Megami Tensei: Digital Devil Saga 2

Completion bonuses:
Complete the game in normal mode, then play again from your cleared game file to keep your previously earned Mantra/Skill, Linkage and Karma Ring. Note: You cannot keep those bonuses if your second attempt is under a different difficulty.
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After starting your cleared game file, reach the battle where a Ghoul tells you that he is wearing a Power Ring. Defeating him to get the Berserker Ring. This item allows you to remain in Berserk mode during a battle without the Solar Data requirement.

Hard mode:
Complete the game in normal mode to unlock the hard mode difficulty. Alternately, load a saved game file from Digital Devil Saga: Avatar Tuner.

Hint: Fight against Girmehkala Sergeant:
Fight a normal Girimehkala but do not kill it. Kill all the enemies that appear with it. Get the Girmehkala's health to less than 25% (red damage text). Keep passing during your turn until it talks about its Sergeant. It will then retreat and be replaced with Sergeant Girimehkala. It is larger, has more health, but has the same attacks, strengths and weaknesses. It is worth more experience points and Atma when defeated.