If we keep the protagonist aside, there are several other film characters whose heartbreaks and character arcs often go unnoticed. Let me present to some such characters and their humble backstories. Their pain has remained insignificant and thus would be an interesting topic to discuss under this prompt! So here goes!
Child Chinna - He was content living in his own world with a like-minded friend circle until he fell in love with a girl. Like every other movie, the hero under the pretext of helping him out, 'overtakes' him and wins her heart. If Child Chinna had been a millionaire like Arvind Swamy in Minsara Kanavu or a Walter White who took revenge on people for stealing his idea, the audience would have still sympathized with him. But he ended up as a fake millionaire only to later help the hero again. His dog was the probably only other being that pitied him and his heartbreak.
Encounter Ekambaram - Being an under-acheiever didn't hurt him much because he really loved his job. Despite everyone ridiculing him and beating him up ruthlessly he didn't give up. Even though I lost hope that he would get a promotion in the near future, he still kept going. Maybe somewhere in the rugged streets of Chennai, he is still spying on the goons and practising how to catch (coins).
Ammavasai - Ullathil Nalla Ullam song cannot sync any better than for Amavasai especially in the scene where his boss uses him mercilessly to help him find out about his lover. You wouldn't forgive any guru-like figure, who has taken his associate to a totally new city, ditch him in a tricky situation and leave him to be beaten up by 50 people. But still you laughed at his pain, didnt you? What has humankind come to?!
Thikku Siva - The Last and probably the harshest one has to be Thikku Siva’s Story cause he is the hero of the film! There were ample reasons why this heartbreak scene would hit us differently- it was the 2nd heartbreak for the hero in that movie and 17373661th for the fans. Yuvan’s bgm, like always, helped elevate the mood. Remember how we write one or two (what we believe) achievements over and over again in our resume when we fall short of ideas? The post heartbreak was something like that. This special heartbreak is not just for the hero, but all of us who watched it.