These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Ashita no Joe
Crowning Moment of Heartwarming: After he returns from juvenile prison, Joe is met with a welcome back party and a newly built gym just for him and Nishi. He doesn't even know how to react, only staring as everybody laughs and dances in front of him. Later that night, while everyone else is asleep, he's crying quietly under the sheets. "This was the first time in his life he had ever felt loved by other people. That was the reason for his tears".
Moral Event Horizon: After Joe humiliates Wolf in the locker room brawl, Wolf retaliates by beating up the neighbourhood children that Joe hung out with. Yeah, while Joe was a terrible Jerk Ass to him, it's not like the kids had a lot to do with that.
Tear Jerker: The death of Rikiishi. Joe finding out Carlos has gotten a severe case of brain damage after his fight with Jose. And of course, the entire finale, where Joe dies.
The first one's specially poignant in the anime, because it also included a BIG Hope Spot. Rikishi won fair and square, Joe aknowledged it and wasn't angry at all about that... and when both loser and winner were about to shake hands...BAM. Rikishi's brain damage kicks in, and he simply drops dead. Cue the Pastel-Chalked Freeze Frame and the narrator explaining what was going on.
In the first anime, to add insult to injury, Rikishi falls with his hand still extended.
And about the third one, well...we all know what happened there. Not helped by how right before dying, Joe gives his bloodstained boxing gloves to Youko and tells her to keep them. Soon afterwards, Joe passes away; when Youko realizes that Joe is dead, she drops them in horror, and everyone starts standing up, and then we have THAT image...
Weird Al Effect: Very few western Otaku have ever seen the original series. But the show has been parodied for so long, and by so many creators, if you've watched a lot of anime, you've seen Joe.