Heartwarming / Adventures from the Book of Virtues
The entire episode of "Perseverance". Seeing Zach and Annie as True Companions in this episode and how they regret their problems with their lessons is just romantic.
Annie apologizing to Zach at the end of "Responsibility", several moments after they refuse to speak to each other.
The ending of "Faith", with Annie praying about her old friend Ruth.
When Zach apologizes to his dad for breaking his camera at the end of "Honesty".
At the end of the third season episode with the same title, Annie invites Zach back to Plato's Peak and gives him a trustworthy letter she wrote.
"Charity". Just "Charity".
During "Compassion", Zach comes across a new immigrant family's house burning down. They lose everything in it, and they can't afford another house. The kid, Emil, is in Zach's class, but Zach is unsure if he should help him, because they never even talked to each other before. The stories Plato tells him during that episode are enough to inspire him and Annie to contact a charity organization so they can help Emil and his family build a new house. The episode ends with Zach gifting Emil with the toy plane he's spent most of the episode playing with.