When Gin has succesfully managed to recruit Benizakura, the latter proceeds to bark towards his owner's house to let him know of his departure. Just as he does however, the boy comes out with a bowl of food and, immediately realizing what's happening, falls to the ground in tears as he pleads for "Don" to stay. When Gin sees this, he recognizes the boy to look like Daisuke, and nearly starts crying as well while fond memories of his former owner pans through his mind. Benizakura himself sheds a tear towards the sobbing boy before turning around and leaving with Gin and Cross, while the boy's devastated calls echoes after them. The heartbreaking score accompanying the scene doesn't exactly help.
Considering the little bastard kid had put Benizakura into a bull-baiting ring, an abusive practice largely condemned as terribly inhumane by most developed countries, maybe the real Tear Jerker should be what Benizakura had to go through to be considered worthy by humans. At least at the end of his life he had the freedom to give it to dogs that respected him and a cause he chose.
Benizakura's death. That dog was a born badass from the beginning to the end. He fights off a bear underwater while the others get away, and you see red blood that looks like that of a cherry blossom. He kept on fighting to the very end, and that's what's really heartbreaking.
Riki's death at the end of the anime. Just when it looks like everything is going to be perfect, and the old man has reunited with Gin and Riki, the bear strikes again and mortally wounds Riki in front of his child. Gin cries and then cuts Akakabuto's head off while still crying.
Gin and Daisuke's goodbye in the last episode. Daisuke tries to approach Gin, but is stopped by the other dogs, snarling at him for getting too close to their new leader. Daisuke complies and settles with simply talking to Gin from a distance, telling him they will always be true friends and he can come home whenever he wants. Through this, Gin is so shocked to see his old human he appears to not know what to do, and can only stare with teary eyes. Daisuke then says goodbye and runs off, leaving Gin to nearly break into tears before being interrupted by his dying father, telling him not to cry as it's a day of celebration.
Right before this, when Daisuke sees the bloody Riki lying on the ground, he chokingly asks Gohei if he's just going to leave him like that, and that they could at least try to heal his wounds. To this Gohei doesn't even turn around, but the camera pans to him crying, as he replies "It's too late. Great men don't want an audience when they die."
Gin yelling "My friends. Victory is ours!" and leading on a mass howling lasting until the snowstorm subsides and the sun rises, all the dogs crying from both grief over fallen friends and happiness of victory, meanwhile it pans to Riki dying just as the rays of sunlight slowly covers his body... and Shouri No Uta starts playing.