Disgaea 3: Absence of Detention

Lonesheep's strategy from the PS3 guide works here:

You may notice that if your character doesn't move but continues to attack from the same spot a combo counter builds up above his picture. Your goal is to get this to 255. Counter attacks will add to the combo. Go to X-Dimension Chapter 1: Strongest Crossroads or any map with contiguous invincibility panels. Kill all but 1 enemy, and then have your strongest character lift the last one. This will prevent the battle from ending yet also prevent the enemy from interfering. Send out two characters with high counter attack rates and have them stand next to each other either the reverse healing panels or the invincibility panels (depending on what map you choose to get the trophy). See the Attack of the Counter 10 trophy to maximize your counter attacking ability. Have the two characters hit each other until the combo reaches 255. This will take a while.