i think you're talking about akikawa and sora? if yes, then they don't really have any background story yet iirc but there are some theories.
so, akikawa first appeared in ch. 44 where he was shown as miyano's co-worker when he got a part-time job in order to buy a gift for sasaki, but he didn't really have a name that time. we only got to know his name at ch. 49 when he encountered miyano and his friends while they were buying stuff for the festival, and they invited him to go. tashiro and akikawa also got along pretty well during this chapter.
ugawa sora is one of sasaki's friends/classmate in college (ch. 46) and we see him more often in the other chapters after that. in ch. 51, it was shown that he also accompanied sasaki to the festival in miyano's school. in ch. 52, it was also shown that sora's hobby is taking pictures when sasaki asked why he took a lot of pictures of the festival.
also in ch. 52, we learned that akikawa couldn't actually come to the festival but he asked tashiro to take photos around the festival with detailed instructions. we saw him again in ch. 53.2 where he was shown announcing to a group of people that he "got the photos". this is where we see that akikawa might actually know sora.
now, this is how they might be connected. in ch. 48, it was suddenly announced that miyano's favorite mangaka will be releasing their new works in a bl event but miyano can't come because he's busy with the preparations for the festival. the mangaka's name was shown in their tweet as "akikawa shouko". miyano then asked sasaki to try and stop him from going to the event but sasaki offered to go for him instead. sora asked if he could come to the event too and so they went together. sasaki asked why sora was wearing a face mask and sora said that some people that he knows might be there. this is where we learned that a friend of sora's actually used to have a table on these events so he's familiar with it. in ch. 53.2, it is implied that akikawa asked for the festival photos because they wanted to use it as a reference which is why he announced to a team of people that he "got" them. because of this, there are theories that akikawa is actually "akikawa shouko", miyano's favorite mangaka, and that sora used to be his assistant which would explain why sora is familiar with attending manga events or why sora's hobby was taking a bunch of pictures, because he was used to taking them to use as a reference. this would also explain why akikawa recognized sora in the one of the pictures.
tbh, my personal theory is that akikawa isn't actually the mangaka, but he might be related to "akikawa shouko" because all this time, the pronoun used for the mangaka was "she". but then again, it might just be one of those pen names artists use in order to not get recognized by people. anyway, sorry for the long reply but that's kind of the explanation to them.
Rereading some of the chaps but does anyone know anything about the people at the end of 53.2?