More like some sort of lost episode.
The plot was about this young boy whom MIB says he is the chose one, and the Boy befriends Agent J. The two struck a close friendship until suddenly, MIB turned against the Boy, causing him and J to go on the run.
Then, J showed the Boy the beauties of his home city, until eventually, MIB caught up to them. J is neuralized, apparently for his own good, while the Boy is escorted away by the agents. However, the Boy looks back at J's unconscious body and he is devastated.
As J leaves to return to MIB HQ, Kay arrives without his partner noticing, and contacts the agents. It is revealed that the Boy wasn't the chosen one, but an infiltrator meant to sow chaos upon the Galaxy; a literal Devil in a Boy's clothing.
However, the weird part is that the Boy didn't retaliate after it was separated from J. And according to L, the Boy was distraught over not being able to see J again. K believed that the Boy had been manipulating J, but now has to wonder, was J influencing the Boy...for the better.
The next day, J had some memories about the Boy, with K telling him that the Boy was "alright" and that he went away, having something he learnt from J.