After Tails is almost literally ripped to shreds while defending the outcasts from Rakghouls he passes out. When he wakes up he finds that Carth has been waiting for him. It becomes heartwarming when you realize that they were on a time-sensitive mission and yet, Carth took the time to stick around and make sure Tails was alright.
After Tails' duel with Bendak, he flees back to the hideout and curls into a ball. Then he gets a verbal ass chewing from Carth and Bastila. The poor boy is an emotional wreck at this point, but when he wants to just go to sleep, Mission offers to sleep beside him. After minimal grumbling, Tails accepts, and Mission snuggles him for comfort. Tails really needed someone to hold him right then.
Tails' managing to help the people of the Undercity find a better future, including the entirety of chapter 047. Tails' dedication to helping the Outcasts of Taris is as awesome as it is heartwarming. Despite first dismissing Rukil as a crazy old man, and his persistent skepticism regarding his fabled "Promised Land", once Tails discovers the Outcast journals and analyzes their contents he determines to give Rukil the data. Then Tails realizes the "Promised Land" is actually a very old landing colony, deep underground and built like a fortress. Tails then goes all out to make the weeks, perhaps months-long trip survivable by repairing the Outcasts' salvaged machines and equipment. The clincher? Tails practically downloads his brain into several datapads so the Outcasts could have his knowledge of science and engineering, and build up their own self-sustaining civilization over the course of several decades. If that doesn't tell you what kind of person Tails is, I don't know what will.
Zelka Forn, too. Tails had only purchased 100 vials of rakghoul serum, at the cost of 2000 credits. But once Tails makes his delivery, he realizes the good doctor sent along nearly his entire stock, nearly one thousand vials of the stuff. Tails wonders aloud if Zelka had bankrupted himself to send so much. Not only that, Zelka had managed to improve the rakghoul serum by including self-replicating nanites, inspired by Tails' own.