Heartwarming / Pokémon Ranger and the Temple of the Sea
When Manaphy first calls May "Mama".
Keep in mind Manaphy is a Pokemon that doesn't speak at all, so it adds bonus points.
Manaphy: Love....you....mama...love you, May.
Basically, every moment May and Manaphy are together that isn't a Tear Jerker.
The time Manaphy used its Heart Swap ability on Ash and Jackie, Ash is momentarily confused. But when he sees that Manaphy is happy, he just smiles back.
Ash gently putting May, Pikachu and Manaphy in a sealed tank, deciding to deal with rescuing the temple alone. Also after almost losing consciousness underwater, he gets a Heroic Second Wind after Manaphy channels a scared May and Pikachu praying for his safety.