The Etecoons of Super Metroid are a trio of energetic space monkeys that teach you how to Wall Jump. If you jump all the way up to the top of the shaft you meet them in, they do a happy dance as if to say "Hooray! You did it!"
Samus can return the favour by saving them before she escapes Zebes.
The Baby Metroid from Super. Who can forget that little chirp it does that can only be assumed to be along the lines of 'Mama?'. And even more touching when it pulls off you after initially trying to kill you, flies around confused... then gives that familiar 'Mama?' sound as it realizes who you are.
Of all things, it's the Critical Annoyance sound from Samus' suit that tips the baby off that you are its "mother".
The Super Metroid 4koma strips feature some cute scenes of Samus bonding with the baby, and the last strip is the two in Samus' apartment, Samus falling asleep under a kotatsu while the baby rests in a little bowl.
A meta example and quite a story. After the disastrous results of Metroid: Other M back in 2010, it looked like Metroid was doomed to be shelved by Nintendo since nothing new came up for Metroid since... Then in 2015, they reveal Metroid Prime: Federation Force which... Simply put, not a lot of people were happy with it and it only made things appear worse for Samus and the franchise. And then in 2016, the game released to mixed reception with many wondering if the series still had a future going for it. The well known fan remake of Metroid II known as Another Metroid 2 Remake also released around this time to many fans joy... Until Nintendo sent the game a Takedown, which only angered, saddened, and confused fans. It seemed like hope for the franchise was lost at this point and that Nintendo just doesn't care about the franchise anymore... But boy could we not be any more wrong because Nintendo decided to finally give the series the love it deserves during E3 2017 with not one, but TWO new Metroid titles. Metroid Prime 4 for the Nintendo Switch and a remake/reimagining of Metroid II for the 3DS titled "Metroid: Samus Returns." Needless to say, it not only pleased many fans, but it also told them that Nintendo still cares about Metroid. And to top it all off, there's even new Metroid amiibo and even a Limited Edition version of Metroid: Samus Returns to boot!
And the kicker? The fans have been asking, begging for new true Metroid content... And Nintendo actually listened.
In January 2019, it was announced that because the game wasn't meeting their standards of quality, Metroid Prime 4 would have its development restarted from scratch by Retro Studios. While this meant that the game would be delayed indefinitely, the overall fan reaction to the delay was surprisingly sympathetic. This is mainly due to not only Nintendo's transparency on the situation, but then recent controversies over crunch time and rushed development among AAA developers leading to games of questionable quality, and that the Metroid franchise had been trying to reestablish its reputation of quality over the last few years after a long drought sandwiched between two polarizing games (helped by Samus Returns and the inclusion of Ridley and Dark Samus as fighters in Super Smash Bros. Ultimate). While news of a delay was disappointing, the fans were willing to accept it as the cost for quality control (especially since The Legend of Zelda: Breath of the Wild, a game that similarly went through delays upon announcement, ultimately became out as one of the best-received games of 2017).