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Tear Jerker: Mega Man Starforce
Mega Man Star Force had the anime episode where Wolf Woods is hiding from Mega Man and the police, so takes on the form of a household dog and sneaks into a house...not knowing a little girl is there. He decides to keep playing up the role of a pet dog to keep hiding, at first hating it, but becoming attached to the girl, and decides to stay with her. This works out until Omega-Xis finds him out at a dog show, and Mega Man battles Wolf Woods, eventually triggering his unstoppable rage, and leaves the girl. He decides that he is too much of a monster to be with her, and gives her an actual pet dog (well, digital one). During the season one finale, when the FM-ians are trying to enjoy their last day on Earth, Wolf Woods goes to visit the little girl...until Gemini kills him for energy. Quite a literal version of Kick the Dog.
There's the Alternate Future from Star Force 2. Dear god, the Alternate Future. The music and grayness makes it worse. The item description even says it can bring a tear to your eye.
The ending of Star Force 3 can be heartwrenching. Kevin Stellar's speech asking Earth to save his son's life would be heartwarming enough, but then you see Hope break down in tears from hearing her husband's voice for the first time in years.