Grim the Legendary Leader

The Legendary Leader prestige class has two feat requirements, Leadership and Iron Will, neither of which Grim has. He will get a new feat the next time he advances a level (to a total character level of 9), and another at 12th level, so the he could enter the Legendary Leader prestige class as his 13th level. By this time his leadership score would be 11 (it's character level + Cha modifier, and Grim's Cha modifier is -2), so he would meet the Legendary Leader's leadership score requirement without needing any more Cha points.

Although there's no problem with it mechanically, Legendary Leader and Warforged Juggernaut are an interesting combination, especially since the Juggernaut has a penalty to checks such as Diplomacy.