Warning: Spoilers Off applies to Heartwarming pages. Proceed at your own risk.
The premise is in itself Heartwarming. Salem being a Doting Parent to Jaune and his sisters is oddly adorable.
When she finds out Jaune ran away, aside from her more humorous reaction of "throw an army of Grimm at the problem," the first thing she does is ask what it was that she did wrong that made Jaune leave. She doesn't blame underlings, she doesn't fly into an unstoppable rage, she doesn't even blame Jaune... she blames herself. It's a far cry from what she used to do in the past, as described by Jinn in the canon universe:blame everyone but herself. Clearly, raising a family gave Salem a sense of responsibility, and Nicholas clearly changed her for the better.
The premise also combines with the later revelation that Salem no longer wishes to wipe out all of the humans and faunus, but simply to conquer them, to create something more heartwarming: the power of love (introduced to her by Nicholas Arc) managed to do what thousands of years of a Forever War didn't and got Salem to stop trying to wipe out her foes. Then later on, she stops the conquest plans too, having a full HeelFace Turn.
Knowing how their relationship will go, the knowledge that some of the first things that Jaune ever said to Yang were about how beautiful she is is very "awww"-inducing.
Ruby and Pyrrha immediately rush off to "save" Jaune from the Nevermore during Initiation. Even if they just met the guy and there is only a slim chance of saving him, neither of these two heroes will give up on trying.
Weiss having a Heel Realization over how much of a Bad Boss she is in chapter 7. She makes up with Pyrrha and Ruby later in the next chapter, and proceeds to become just as good a leader as her Grandfather would have wanted from that point forwards.
Jaune immediately going to help Velvet while she is being bullied by Cardin. This heroic action makes Velvet get a crush on him.
Mercury being embarrassedly pleased when Jaune praises his prosthetic legs. He later remembers this event to call Jaune "pretty cool" and is genuinely friendly with him.
Mercury's character growth in this story is pretty neat to read about as well, seeing as how he actually starts making real friends, rather than just "People he has to work with," or "Contacts."
Everything about Yang and Jaune's relationship definitely counts. The two are adorably awkward around each other, especially Yang.
When Jaune thinks that Yang asked him on a date (asking him and Ruby to come play video games in her room and ending the affirmative response with "It's a date",) he brings her a big bouquet of flowers. Yang's flustered response is beautiful to behold.
Nicholas Arc even gets an indirect one, as when Jaune offers to get Yang more flowers, Ruby asks who tries to get people flowers that often. Jaune, without hesitation, replies that his dad does for his mom. Suddenly, Salem falling for the man seems like it happened for more reasons than just sex...
On their second "Date," it starts out In Media Res with Yang freaking out because it was another accidental date set up by herself. She's confused, doesn't want to hurt her sister's feelings, and is blanking on any sort of response... but at no point in her mental debates does she let go of his hand.
Even though Qrow set it up to fail by telling Jaune to play it super-formal, Jaune and Yang's date goes amazingly. Part of the credit goes to Yang having never really been on a date before, and her being tickled pink at him just treating her like a princess.
Because they're in a five-star restaurant and she's in her prom dress, Yang is getting funny looks. When she points this out, Jaune points out that yes, of course they're staring at her. Yang feels hurt and says that he shouldn't point out how out of place she is, she already knows- except then Jaune says that they're staring at her because she's the most beautiful woman in the room.
Yang's whole plan for the date was to have some fun, but eventually let him down gently and tell him to ask Ruby to the dance. The date goes so well, she completely forgets about that plan until Blake reminds her back in their room.
Yang finally confessing her feelings to Jaune at the dance is a combination of funny and this, particularly since she was crying earlier.
She tries to tell him to take someone else, trying to get him to like Ruby one last time, only for him to reply that for him, there's no one else he would even think of asking if he couldn't ask Yang.
Team RYBN is just like a loving family. Nora, Ren and Yang basically stop Blake's self destructive habits from canon by simply attaching themselves to her and not letting go. She trusts them so much that she tells them about her being a Faunus. They knew already.
Cinder's relationship with Jaune. While she's definitely not as nice as Jaune thinks she is, she definitely loves him though what kind of love is debatable, and is at first so focused on helping Jaune while at Beacon she honestly forgets about her mission. Meanwhile Jaune has nothing but praise and respect for her and his go to solution for problems is often 'What would Cinder do?'.
In a similar strain, even Salem is shown to deeply care for, and love her family, and is willing to do anything in order to protect them. Likewise, Jaune constantly expresses his affection and admiration for his mother.
Salem being overjoyed Jaune finally called her in chapter 55, her behavior and wording showing once again her love for her husband and children is entirely genuine. Even gushing at her son in a typical embarrassing mother fashion that causes Ruby to giggle.
When Ruby up and asks who, and in a veiled implication, what Salem is. The Queen of the Grimm's response? "A mother."
Despite Ruby all but figuring out Jaune was Hentacle and thus heavily suspecting his mother was a "grimm-person" as well, Ruby doesn't rat out Jaune or Salem after Jaune embraces her and confirms she's his best friend.
What does Jaune do when he sees the injured Yang whilst locked into his grimm form during a Unstoppable Rage? Cradle and nuzzle his "mate". Even in his berserk fury, he still recognizes Yang and their friends.
Ruby forcing Jaune to look at her, even when in his grimm form causes him to calm down and listen.
Pyrrha declaring she has feelings for Jaune despite him having a girlfriend and being told he is part grimm. In an ironic twist, it saves her life due to a Nevermore catching the conversation and ferrying it to Salem.
All of Yang and Yin's relationship, especially as she goes from freaking out over his existence to considering him her son.
Yang and Jaune's reconciliation in chapter 76. It's handled very well, and both sides don't know exactly what they're supposed to have done. Yang is furious for Jaune running out on her, feeling abandoned and seeing reflections of what Raven did when she left Taiyang, which isn't helped by her feeling like Jaune got her pregnant when he left her Yin (not to mention the faint sense of violation or the emotions that having a child is giving her). Jaune can only reply that he didn't know what else he was supposed to do and gave her a means of protecting herself, which he couldn't provide since Ruby and Nora didn't trust him at the time with Yang (having recently learned his heritage). As for why he didn't tell her about the Grimm thing, he was scared that everyone would either leave him or kill him, and it's clear he wasn't emotionally ready to deal with either of those things. While the conflict isn't resolved, and it's clear that there's going to be more rocks on the road ahead, it feels very natural and sets up the idea of them getting back together. Also at the end he softballs a marriage proposal to Yang, offering to make her Queen of the Grimm (though how much of that was intentional and how much was him being unaware of the implications of his offer is up for debate).
When she calls him out for constantly saying that he didn't know what to do or that he was unaware of something, he pulls her into a "Shut Up" Kiss and tells her that if he knows nothing else, he knows that he loves her and wants her to know that.
Jaune does his best to save Pyrrha's life from gaining the Maiden powers, because he knows Cinder will kill her to get said powers. He goes with every detail he knows from Pyrrha's life and convinces her that the power would make her miserable, that it'd be more of everything she ever hated about being famous, and he's sincere about it. It actually works until the White Fang attack makes her take them up anyway.
The idea of some Mother-Daughter (In-law) bonding is enough to snap Salem out of her Unstoppable Rage and gleefully demand some wine and ice cream so she and Pyrrha can chat.
Pyrrha, when drunk, evidently has taken quite a shine to Jaune's pet beowolf Mannie. When Salem questions Pyrrha if she thinks all grimm are evil and cites Mannie, Pyrrha handily denies it and cuddles him like he was a giant puppy.
Salem's diabolical plan for Pyrrha? Show her Jaune's baby pictures. She and Nicholas kept extensive copies of pictures of their children, and the pride and love she feels in her children shines through clear as day.
Jaune threatens a war between the Grimm and Atlas after they kidnap Yang and Yin. In his announcement, he declares that she is his fiance, and that she has his child with her. While it was for political points and to get sympathy on his side, Jaune officially declared that he and Yang are betrothed and that he accepts Yin not only as his son but part of the family.
When Ozpin tries to pull The Needs of the Many during the Battle of Haven, everyone present tells him where he can shove his ideas, they're not abandoning their friends/family.
Raven admits that while she knows Qrow and Yang want nothing to do with her, she'd still use her portals to save them if things go south in Atlas.
Salem's final plan for herself: Find a way to grow old and die with her husband.
Nicholas Arc, despite being a hunter, shows absolutely nothing other than pride and love for every single one of his family, even Cinder, who is adopted. In this story, he settled down in Ansel and bought a house away from the town because he hoped one day, his whole family- including Salem- could come and visit him there, away from the Grimmlands.
Ozpin eventually realizes he was in the wrong and concedes to Nicholas Arc both in regards to his war against Salem and his former relationship with her. Upon being offered, Ozpin states he'd be honored to meet their daughters.
Nicholas, near the end, has a scene where he's tossing one of his youngest daughters in the air again and again, and other than her having tentacles out, it's exactly like what you'd expect from a father lovingly playing with his daughter.
When asked if it bothers him that Salem used to be married to Ozpin and had a family with him, Nicholas tells Ozpin "it doesn't matter how many people a woman has been with, only who she chooses to spend the rest of her life with".
This actually goes a little deeper- In Coeur's stories, characters will tend to have the same backgrounds unless otherwise stated, meaning that Nicholas Arc will have the same backstory even in different stories, and Jaune's siblings will remain the same (speaking generally, of course- there's obviously going to be some differences in worlds with obvious changes, like one where Juniper Arc is Salem or they're based on RPG mechanics, but for the most part it's the same). This same piece of advice was actually first shared in the story "One Good Turn Deserves Another," and was referenced again in "Service with a Smile." This isn't just something that Nicholas feels in this one instance, this is a core aspect of his character that translates across the multiverse.
One for Nicholas and Salem? Even though this is a comedy story, and it would make perfect sense for there to be some tension between Nicholas and Salem (given their respective roles), at no point in the story do they ever seem to argue or get mad at one another. Now, the sex might be part of it, but from the way they interact, there's a lot of trust, respect, and open communication between them. Overall, despite how it started (and how one of them is essentially the Remnant version of the Devil), their relationship is one of the healthiest in the entire story.
Here's another one in the grand scheme of things. Given Salem's past in canon, the very fact that one random act of love from Nicholas Arc can leave massive repercussions, from redeeming the world's most dangerous threat, to birthing a hero who will forge world peace between humans and Grimm, can be very endearing to many. It also takes off the stress from Oz himself, who, after spending countless millennia as a Shell-Shocked Veteran in an eternal war against Salem, can finally relax as he won't have to worry about the future of mankind thanks to Jaune's efforts.
While visiting Beacon, everyone avoids Ruby and Pyrrha due to their connection to Grimm royalty. Except Coco, who casually walks over and sits down next to them, prompting others to do the same.
While watching the above, Mercury and Velvet playfully rib each other.
Taiyang's biggest problem with his oldest daughter apparently marrying the Crown Prince of the Grimm and getting knocked up by him? He wasn't invited to the wedding.
In Chapter 99, Ozma and Salem finally manage to reconcile.
Chapter 101: Jaune and Yang have their first time together.
When the God of Darkness removes Salem's and her children's control over the Grimm in an attempt to turn the Grimm against them, the Grimm pause only briefly before continuing to attack him.
Darkness: How? They were stripped from your control! Sapphire: And why should that change anything? Do you think they were slaves? I grew up with one-hundred thousand siblings. I played with Beowolves, cuddled up by Ursa through the night, rode on Deathstalkers, and helped Nevermores preen those hard-to-reach spots. We all did. There wasn't a day that would go by when we didn't feed the Grimm, pick sharp rocks from their paws, or play with them. You abandoned them. We did not. What choice did you think they would make?
When the God of Darkness defeats his brother, everyone present swears to honor their bargain and worship him as their god, including a festival and tournament held annually in his honor. Darkness looks downright eager to actually have worshipers.
In the penultimate chapter, Yang accidentally interrupts Ruby's attempt to confess her feelings for Jaune, but also tells Ruby that if she was willing to share with anyone, it'd be her little sister.