Alien Knuckle's defeat in his second fight with Jack.
The finale of Ep. 1, when Ultraman talks to Goh, who then begins to understand his role as a human host.
Goh's selflessness, a prime example being Ep.2's rescue in the oil refinery. Earlier in the episode, Goh got a teammate hurt and he himself was suspended from MAT for being impetuous. Capt Katoh realized then what an asset to the team Goh was.
In Ep. 1, Ultraman Jack hovers over Goh in his hospital bed, explains what just happened and what Goh did that impressed him, and fell into Goh! A little Nightmare Fuelish, but still cool.
The Ultra Bracelet saved Jack's life in Episode 40.