The Urthblood Saga/Heartwarming

Cyril's devotion to his brother when he's wounded by Smallert. When he sheds tears of joy at his recovery, leading Geoff to point out how he claimed earlier that true warriors don't cry, he responds: "Then I guess I'm no warrior... But it doesn't matter. Cyrus is going to be okay, and that's what matters.
When a rat soldier staying at Redwall gets queasy at hearing what Urthfist plans to do to his kind if they ever get into Redwall, Foremole goes to put a comforting paw around his shoulder, assuring him everything is going to be alright. It's a small gesture, but it shows how far the Redwallers have truly come in regarding vermin as anything other than enemies.
The story of Smallert's acceptance into Redwall. Having killed one of his fellow soldiers and nearly killed Cyrus in a rage due to Wolfrum's provocations, at first it appears he's condemned to die for his actions. However, his obvious remorse and shame over his mistake moves the Redwallers to the point that they convince Machus to spare him, discharge him from the army, after which he's adopted by the abbeybeasts. Not only that, but Cyril, the very mouse he so grievously wounded, forgives him and they eventually become close friends!