The following is Open Game Content from a 3PP Source
Sojutsu (Ex): Sojutsu is the art of spear-fighting. The samurai that specializes in sojutsu gains Weapon Focus: yari and Exotic Weapon Proficiency: bisento. They study both how to defeat a charging enemy, and also how to use their own weapons in a charge attack themselves. At 5th level, they deal double damage when charging with their spear. At 8th level, they do 3x normal damage when set to receive a charge and gain the Run feat. At 11th level, the samurai does 3x normal damage when charging. At 14th level, they do 4x damage when set against a charge and take -1 damage per die of damage from charging foes. At 17th level, the samurai does 4x normal damage during a charge attack and takes -1 point of damage per die of damage from foes set to receive a charge.
At 11th level, the samurai gains the Advanced Style of naginatajutsu, which grants them the Exotic Weapon Proficiency: naginata and the samurai can use the naginata in charges or against charges, just as they use the yari or bisento.