Yakuza: Dead Souls

The maximum character level is Lv 99. Luckily all characters share the same experience pool so whatever level one character is, the other characters will be that level as well. Experience, levels and abilities are carried over in Premium New Game.

This will be a long grind and it is recommended that you equip the Yakuza Training Gear on your 3rd playthrough on Extra Hard. This item gives you an extra 20% experience at the expense of reduced attack power. It can be exchanged for Directive points from Hasegawa in Cafe Alps.

The best method thus far is to play Hasegawa's Spec Ops mission as Kiryu. The second Spec Ops mission will put you up against 5 Aggros in a small room. Each of them is worth 800 XP (960 XP with the Yakuza Training Gear). With the Satellite Laser obtained from defeating Amon (see Amon's Vanquisher trophy), you can take all of them down in less than a minute. This translates to 4800 XP approximately every minute so it takes about 20 minutes to gain 78000 XP which is equivalent to 1 level starting from level 86 onwards. If you ever run low on health just speak to the waiter in the very same Cafe Alps to dine in and restore your health.

Glitch: You will not unlock this trophy if you reached Level 99 by gaining experience through eating food/dining at restaurants.