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Zero[]
"Thanks for 1,500,000 Subscribers!", when Five asks about the whiteboard, Zero is prompted to explain the new subcount.
In "Thanks for 2,000,000 Subscribers!", Zero is ticked off at the fact no one updated the subcount. Five asks why they care so much to which the response is that since the Zeroes had to do their time, it was now the other integers' turn.
In "Thanks for 2,763,000 Subscribers!", after seeing Six and the other Zeroes laugh at their leader's tapes, Five decides to enjoy themself as well. Zero tries to convince them otherwise, but Five decides that they want a break.
After Zero destroys the TV, he and Five argue over the situation; Five complains that they cannot find the correct tape anymore, while Zero replies that if they wanted to, they would have done so already.
Three[]
In "X Finds Out His Value", Three and Five are seen playing ball in the opening scene. However, Five drops the ball and frowns. In "The Number Playground Chronicle!", Three is "foaming" in anger due to Five not picking up the ball. Three later writes an article about "Catch!" where they say that they'll "catch Five if it's the last thing they do" due to them not picking up the ball.
Four[]
In "Return of the Rocket Ship", Four is enraged when Pen states that five is greater than four. Likewise, in "X Marks the Spot", Four refuses to let Balloony do a high five. Although these were almost certainly throwaway lines and probably do not mean anything related to the actual character Five, they can be considered in retrospect as an extension of Four and Five's relationship to each other.
In "Thanks for 1,000,000 subscribers!" Five initially goes along with Four's idea of playing a game, before asking themselves why they're doing this, and asking Four what he means.
Later, when the first elimination of Battle for Permission to Meet 10 takes place, Four announces Five as being eliminated. Five is angered by this, since there was no voting and they never lost a challenge. In response to this, Four makes up a challenge on the spot, don't be a purple number five. Five loses the challenge and is announced to be eliminated.
Before Five can leave Four stops them, telling them that for this elimination they'll be doing "a classic.", where Four will suck up Five, akin to Battle for BFB. Five objects, but Four does it anyways. Five tells Four to stop as they attempt to suck them up.
Six[]
In "Thanks for 1,000,000 subscribers!", when Nine suggests that Six take their place in the subcount, Five tells Six they shouldn't listen to Nine, since Nine is going to make them handstand in the subcount again.
Later, when Five says they'll go retrieve Ten, Six seems impressed that Five knows Ten personally. Later, the two briefly argue over who gets to go retrieve Ten.
When Five escapes being sucked up by Four, Six laughs at them due to how they look, with Five telling Six to be quiet.
In "Thanks for 1,500,000 Subscribers!", in contrast to Five's usual tendencies to denounce cannibalism, they notably do not care after "Fifteen" claims to have eaten Six and Nine.
Later in the episode, Five refuses to add with Ten, instead stating that it is Six and Nine's responsibility to deal with the subcount.
In "Thanks for 2,000,000 Subscribers!", when Six mentions updating the whiteboard, Five accuses them of stalling their Jenga turn.
In "Thanks for 2,763,000 Subscribers!", they try to get into the vent Six has hidden themself in, first by begging and then by force. After managing to break through themselves, Five enters Zero's base and begins to reprimand Six, among other things, calling Six irresponsible and all the years the two have known each other "painful", before being distracted by the videos.
Seven[]
In "Thanks for 900,000 subscribers!", Five is confused when Seven makes a reference to the "seven ate nine" joke. Considering the joke disgusting, and reminding Seven that they do not promote acts of cannibalism in a law-abiding society.
In "Thanks for 1,000,000 subscribers!" subscribers, when the Algebraliens are telling stories about how Ten saved their cats from trees, Seven is reminded of a time Ten helped them. Five, irritated, guesses that Ten saved Seven's cat from a tree, only for Seven to reveal that they were the one being saved.
When Five brings up how they and Ten talk all the time, Seven calls them a liar, saying that Five doesn't have any friends. Five responds by saying that they do have friends, with Seven telling them to name one. The two start to argue over if Five has friends or not.
Nine[]
In "Thanks for 900,000 subscribers!" Five calls Nine's presence annoying.
In "Thanks for 1,000,000 subscribers!", Five tells Nine to be quiet when they complain about standing in the subcount, considering Nine a baby for whining in the first place.
In "Thanks for 1,500,000 Subscribers!", in contrast to Five's usual tendencies to denounce cannibalism, they notably do not care after "Fifteen" claims to have eaten Six and Nine.
In "Thanks for 2,000,000 Subscribers!", Five is annoyed by Nine keeping a bag over their head, and tells them to take it off, to which Nine refuses. They also point Nine's face when it does come off.
Ten[]
In "Thanks for 1,000,000 subscribers!", Five claims that they and Ten talk all the time, which is disputed by Seven.
In "Thanks for 2,763,000 Subscribers!", after managing to get through the vent, they leave Ten at the mercy of Fourteen, ignoring his pleas of help.
Fourteen[]
In "Thanks for 1,500,000 Subscribers!", Five is concerned upon hearing of Fourteen's habits, asking if they should do something about that.
In "Thanks for 2,000,000 Subscribers!", the mentioned scene is shown in a flashback, the context implying this is what got Fourteen imprisoned. Later on, he manages to fool them successfully, allowing for his escape. Five is also one of Fourteen's prank victims, stepping in gum Fourteen placed on the ground.
After Fourteen eats Ten's skin, Five is the one to come up with the plan that defeats him. They punish him by having him write the subcount, stating that they may let him go if he behaves well.
Fifteen[]
Although the actual characters have never directly interacted, in "Thanks for 1,500,000 Subscribers!", Five shows notable excitement upon seeing what they think is Fifteen.