A minor one, but during Oga's fight with Tojo when Baby Beel attempts to assist him with demonic powers, Oga tells him to knock it off and comments that: "Even if I didn't have this contract, you know I'm not going anywhere." It's ESPECIALLY potent in context with the story arc, because previously Beel had severed the contract between him and Oga to prevent Oga from being killed. The minute he did, Oga left. Wonder if he'd do the same now?
Hilda thanking Oga for protecting her when she was seriously wounded by Hecadoth.
In Chapter 75.5, there's this line by Oga.Made poignant because Beel was trying to be a man and defend a cat, who he saw as an enemy before.
Hilda calling Oga by his first nameafter getting her memories back. And it seems she'll be doing that from now on.
Kanzaki really does care for his little niece, as seen when he punches Oga in the face for making her cry.
Even though they're rivals, when Shizuka's brothers knock Kota down and steal his hat, Beel gives him his own hat to wear and tells him (in baby terms) they're going to fight together.
Oga has one of his rare kind moments when standing with Hilda while looking up at a portrait of Beel's mom. The wetnurse remarks that one day she would like Baby Beel to meet his real mother, and Oga replies by saying that Hilda is his real mother. Hilda, of course, pretends to brush it off but is visibly touched by his words.
After Furuichi tells him he's tired of being called a loser and a pervert and knowingly uses demon powered tissues that threaten to kill him with prolonged exposure in order to win for once, Oga remembers that, the first time they fought, Furuichi's sheer determination made him one of the strongest people he'd ever faced. It's the first time Oga has shown genuine respect for someone.
Also that they were willing to forgive him for his being a jerk (Kunieda even said he had a fever that made him crazy as an explanation for the demonic tissues).
"Hey, who told you that I'd stand behind you? I'll stand right next to you."
It's sweet enough that Oga tells the Red Tails to stop bullying Furuichi (because while he's weak and annoying, deep down he's tough) but then there's their reply.
Nene: What are you saying? We know that already.
Finding out that Kazuya and Azusa really do have a crush on each other but have been too shy to admit it.
Looking at how far the Ishiyama Gang have come, from being bitter enemies who squabbled and stubbornly refused to have anything to do with each other to displaying teamwork and even the seeds of friendship. The alliance against Akuma Academy to avenge one of their own is a start, but it becomes especially obvious when they willingly meet up to discuss their tactics against Nasubi without a second thought.
In Chapter 193, Kanzaki of all people telling Nasubi not to talk shit about Oga, who he finally admits is his boss. Even the resident Miles Gloriosus is willing to admit that Oga is better than him and worthy of respect, and Oga for his part tells Nasubi not to underestimate his underling. Coming from delinquents like them, this is as good as them admitting that they are True Companions.
Although Oga treats Furuichi like trash, the quickest way to push his berserk button (not including Beel) is to mess with Furuichi.
Case in point: first two pages of Chapter 207. A guy mocks Oga about beating up Furuichi, who is down on the ground. Oga says nothing and jump kicks the guy in the face.
When Hilda gives Furuichi the Demonic Tissues, she tells him to take care of both Baby Beel and Oga. She'd never say it to his face, but she does care for him.
Hilda does the same for Furuichi, although she treats him like the plague. She was worried when she discovered the harm the Demonic Tissues were causing him, and was angry that Oga was letting Furuichi unknowingly kill himself.
In Chapter 226, it's revealed that Iris, Beel's mother, is with the Solomon Company, and there's a good chance that she's a traitor to the Demon World. Given the way Hilda looks up to the woman, she takes it pretty hard and even loses her cool, which happens very rarely. Furuichi immediately tries to cheer her up by saying they should go to America to get some answers from the woman. All the other times Furuichi has tried to act cool in front of Hilda (or any attractive girl, for that matter), he would be imagining her throwing herself at him in gratitude and/or admiration. Not this time, though. This time, he just wants to help out a friend who's going through something rough. And then we get Oga's response:
This moment's really great because a) it shows how close Furuichi is to both Oga and Hilda and how much they genuinely accept him and value his input, and b) it shows just how much Oga cares for his family. He truly sees Beel as his child and, though he may not understand all that it entails, he truly thinks of Hilda as his wife. And what he says next is even better, because it shows just how much of a Papa Wolf he's become:
Oga:However... If I were going to give my two cents to the woman that had you and then dropped you like a bad habit, that's a different story. Right, Beel?
On a similar note to the above, in Chapter 225, there's a really great yet subtle moment between Oga and Hilda. While Hilda has an adorably affectionate side, it tends to be reserved for Baby Beel, and even after Oga saved her from Behemoth's men and she got her memories back, Stoic Hilda (not Amnesia Hilda) would still remain rather guarded around him at all times. In Chapter 225, however, she excitedly tells him that the scenery in America looks a lot like that of the Demon World. It's the first time Stoic Hilda readily opened up to Oga and shared something with him, and it shows just how far the two of them have come. What he said to her earlier in Chapter 226 must have really meant something to her. She also agreed to and was quite enthusiastic about cosplaying as a ninja with Oga (he's dressed as some sort of samurai) in Chapter 228, going so far as to call herself the sexy ninja. To put this in context, even Furuichi, Oga's lifelong buddy, had reservations.
When Fuji is turning the whole city to stone, of course the gang is going to save Oga. But a lot of them, including Kanzaki and Kunieda, also are willing to put themselves on the line to save Furuichi.
Kunieda might not have been there, but she knows the real reason Oga gave Beel up. And finally confesses her feelings.
After the battle the Demon King nukes the enemies headquarters for hurting his wife. And seeing his son surrounded by his loved ones, decides the whole world wasn't so bad after all.
The epilogue is made of heartwarming, and the final word is Beelzebub's: he's learned how to say Furuchin, Oga's old nickname for Furuichi.
Furuichi is seen getting respect from the whole school, and calls his friendship with Oga and the events of the manga the happiest days of his life.
The Demon King trusting Oga with caring for his newborn daughter, and Oga fully willing to accept that responsibility (in contrast with his initial attitude towards raising Beelzebub) is pretty heartwarming.