Shinso and Ojiro are barely shown interacting in the anime or manga.
Their only canon interaction is during the Sports Festival Arc, when Shinso uses his mind control quirk to use Ojiro for his cavalry battle team (along with several others). After the cavalry battle is over and Shinso's team moves onto the next event, Ojiro resigns from the festival because he does not feel as like it was fair that he should be allowed to compete in the next event, since he has no memory of participating in the previous event.
Ojiro later warns Deku about Shinso's quirk because he doesn't approve of Shinso's method of winning.
During Shinso and Deku's battle, Shinso insults Ojiro by calling him a "monkey" and saying that he kept "going on about his pride" and "he was dumb for throwing away his chance."
In the manga, during the battles between 1-A and 1-B, Shinso reappears and Ojiro is shown to look irritated by his appearance. They do not officially interact, however.
Though they don't have much interaction in canon, ShinOji seems to have a decent following within the fandom.
Most of their following comes from the idea of Shinso apologizing to Ojiro after the sports festival and eventually becoming friends with him.
With the 1-A & 1-B battle arc involving Shinso in the manga, the idea of them becoming rivals or sparring partners also became a popular idea.
Another idea within the fandom for this ship is their similar yet different personalities. Both are more on the side character side of the show, but as their personalities are shown Shinso is a tired type personality yet can be very tough when determined, on the other hand Ojiro is shown to be a very laid back character who can stay calm in most situations, while still maintaining a fighting spirit. They both can be very tough in their own was when it comes to being determined which is where the idea of their fun dynamic comes from.
An upside to both of these characters not being shown often, is that while we can see the base of their personality there's always room to develop fanon parts and explore more into these characters.
- Their Japanese ship name is "心尾", which roughly translates to "heart tail" in English.