- The ending of "Lab Friends... Forever?", Billy, Zeke and Marsha having their own little slumber party (complete with pillow fights) after Marsha misses hers on earth.
- On top of that, Zeke and Marsha finally acknowledge Billy as a friend instead of just a lab partner.
- Actually, the trio's relationship as a whole is this. Having formed initially just so they could pass science class and achieve their own seperate goals, their time and experiences together in Subterranea-Tania have gradually made them into True Companions.
- The plot of "The Date", Zeke and Billy trying to cheer up Marsha (who missed her chance to reunite with her summer crush) with a makeshift romantic dinner date is pretty sweet.
- In "Calzones", the ogre chef complimenting Zeke's cooking, saying that his calzones were the best he's ever tasted.
- A meta-example: this drawing Aaron Springer did for Catie Wayne (voice of Marsha) on her 25th birthday.
- Billy in general is just a big ball of heartwarming. The fact he would do anything to help and save his friends is quite Admirable.
- In "Sluggy", the montage of Billy and Sluggy bonding is surprisingly adorable to watch.
- While it's an off-hand comment, the story Marsha mentions in "Rat's Entertainment!" about when she was little (she was suffering from an "oozing rash", so her parents put on a musical to show how much she meant to them) is rather sweet.
- The entire episode is one, with the people of Subterranea-Tania (even the villains) coming together to cheer up Anaximander, who repays them with a rockin' guitar solo.
- The ending for "The Battle For Subterranea-Tania" is really sweet. Especially when the citizens of Subterranea-Tania praise Billy and actually admit that he's a friend. (Or at the very least "Okay", for those those who don't really get along with him.)
Heartwarming / Billy Dilley's Super Duper Subterranean Summer