First, there is Union 5-3392 who is described as sickly and prone to having convulsions. At one point, he has an attack while at work and the other two friends allow him to sit in the shade while they finish all the work for him. Without that, he probably would have gotten trouble for slacking on the job. This also shows that even though friendship was outlawed, people will take care of each other in their own selfless ways--it doesn't need to be forced upon one another.  Then there is International 4-8818 whose personality shines through his evident laughter. Equality 7-2521 admires International's ability to remain true to his laugh even when it is not required of him. International is also a loyal friend to Equality 7-2521 even though he knows that by keeping the secret of the cave he could face fierce punishment. Both friends have unique character traits that help the main character to distinguish them from himself and to find the individual in himself as in everyone else.