In "Long, Tall Daggy" Norbert takes great pride in being slightly taller than Daggett, and in fact makes it a weekly tradition which he calls Measuring Day. Then one day, the automated measuring chart shows Dag to be the taller sibling. Naturally, Dag lords it over Norb and doesn't seem to take notice as his brother's self-confidence crumbles over the course of the episode. Come the next Measuring Day, Norb finally admits to Dag that he can't handle the fact that he's now the shorter brother. Dag brushes it off ("Well, that's just tough newbies, Norby!") and they march over to the measuring chart... But Dag drops to his knees to get an inaccurate reading. While it's a little dishonest and hides the truth from Norb, Dag really does care about his brothers' feelings.
Until you realize that the difference always seems to be about the same except for the first time and this one, meaning Dagget has been deliberately causing an inaccurate reading all this time. Heartwarming indeed.
Dag's single-minded determination to be a good "mom" in "Daggy Dearest" despite the fact that he's a boy and the baby he's caring for is a mongoose is slightly endearing considering his usual brand of stupidity extends solely to Norb and "Gary" isn't harmed or mistreated in any way while under Dag's care.
At the end of the episode "Fakin' It", after Dag tricks Norb into thinking he has the beaver gargle of ache, Norb gets angry with him, Dag states that Norb tricked him first and that he cares for him, Norb then says that he cares for Dag too and Dag says he's the best big brother in the whole world and the two then hug.
Its also sweet to see Dag looking after Norb and doing anything to make him feel better.
In "Stump's Family Reunion", when Norb is acting weird due to problems with his ear, he kisses and hugs Dag and calls him beautiful which was extremely cute.
Dag also kissed Norb at the beginning of "Oh, Brother?" and says that he loooooves him.
Norb reassuring a terrified Dag over his fear of crickets in "Bug-a-Boo".
Later, Dag deciding to let the cricket go when he realizes that it's as scared of him as he is of it.
When Norb finds out that Dag may not be his biological brother, Dag is completely unfazed by the revelation while Norb is shocked. When Norb asks Dag why he's not more shocked at this, Dag simply states "To me, a brother is someone you grew up with and who LOOOOOOOVES you!" and remains strong in this assertion throughout the episode. A surprising moment of wisdom from a character who's frequently presented as an idiot.
When Norb and Dag's "real" brothers show up at the dam, Dag is adamant that he doesn't consider Randy (who is essentially an even stupider, imbecilic version of Dag who can only laugh) his brother, he still has a lot of fun with him while Norb and Byron (who is essentially a smarter and haughtier version of Norb with a ridiculous overbite) are miserable (in that Byron keeps belittling and manipulating Norb).
From "Stinky Toe": Dag working under the 24-hour time constraint to find the cure to stinky toe after Norb contracts it because the other scientists will launch Norb and all the other beavers in the world into outer space if Dag can't cure him.