I was looking over this class again and I came up with a couple ideas.

I think that Elemental Affinity requirement should be removed from the Phlegm. The ability to cause a status effect with damage is too good to limit to just those who are geared to a specific element. Instead, the ability would have a Kaijin level 5 base requirement and deal d4's of untyped damage. Those with Elemental Affinity would be able to substitute their EA damage instead. Examples of how this would be written are in the following abilities I came up with:

"Spines, Maybe?" [Monstrous]
Prerequisite: Kaijin level 5
Benefit: The Kaijin is capable of launching a barrage of projectiles at a single foe. As an attack action, you may make a ranged attack against a single target within 30' of the Kaijin. This attack does 1d4 damage. At 9th level and every four levels after, increase the damage die by 1.
Special: A Kaijin with the Elemental Affinity ability may substitute the damage done by this attack with the damage granted by Elemental Affinity.

"How About More Spines?" [Monstrous]
Prerequisites: Kaijin level 7, "Spines, Maybe?"
Benefit: The Kaijin can now target multiple foes with projectiles. As a full-round action, you may make a number of ranged attacks, up to the maximum allowed as permitted by BAB, against any targets within 30' of the Kaijin. This attack does 1d4 damage. At 9th level and every four levels after, increase the damage die by 1.
Special: A Kaijin with the Elemental Affinity ability may substitute the damage done by this attack with the damage granted by Elemental Affinity.

"Okay...A LOT Of Spines!" [Monstrous]
Prerequisites: Kaijin level 9, "Spines, Maybe?", "How About More Spines?"
Benefit: The Kaijin is now capable of unleashing a burst of projectiles at every opponent around him. As a full-round action, you create a burst of projectiles that hits each creature within 20' of the Kaijin. This attack does 2d4 damage. At 13th level and every four levels after, increase the damage die by 1. Reflex DC (10 + 1/2 Kaijin level + Con modifier) for half damage.
Special: A Kaijin with the Elemental Affinity ability may substitute the damage done by this attack with the damage granted by Elemental Affinity.