After killing the evil plants, he will make healing powder; if brought a broc flower and a xander root, that is. "Beware," he says, "for they fog the mind as they cleanse the body", and as usual, is right on target, despite his apparently permanent trance state; each healing powder reduces Perception by one for six hours.
Hakunin will appear to you in several visions you have when dreaming, telling you about the dying village and the Enclave attack, suggesting Hakunin has some manner of psychic abilities.
There are four dream sequences scripted in the game code to occur on the 23rd of October 2241, 21 January 2242, 21 April 2242, and 20 July 2242. The last is also scripted to occur as the player leaves Vault 13; any remaining scripts are then nullified and those visions will not be seen.
After this last dream, if the Chosen One returns again to Arroyo, the bridge map is changed, Arroyo becomes inaccessible, and Hakunin is seen in a separate talking head sequence (where he is laying on the ground with most of his tribal headgear smashed, he is covered in blood and talks in a rasping voice.), telling the Chosen One to go south, which is the general direction of Navarro. (See also: Timeline)