Purvi - a girl with hang-ups. She is adopted, feels unworthy of love and being loved, makes up for it by being aggressive at work and succeeding but has this innate desire to prove to the world that she is indeed worthy of being cared for by a mother like her Aai. Arjun comes along, supposedly falls head over heels in love with her and she cannot believe her reality. He is to be betrothed to Ovi, her mother's natural daughter, the girl who has it all in Purvi's eyes (just by the merit of being Archana's natural born) and he has chosen her, Purvi? The deal is proposed by Ovi and Purvi perhaps still not believing she is worthy of being loved over Ovi by Arjun, proposes, nay forces, Arjun to marry her "sister". Maybe she has a faint hope that if he truly thinks her, Purvi, deserving especially after the night at the hut, he will rant and rave but decline to marry Ovi. He goes ahead and marries Ovi, proving (in Purvi's mind at least) that when push came to shove, she really was not good enough. Later matters get to a head when Ovi accuses her of trying to have an affair with her husband. Purvi is left with no choice but to tell Arjun to move on "if he truly loved her" (a last ditch attempt to convince herself that he does in fact really love her), not realizing (or perhaps realizing) that a man truly in love would never be able to move on, at least not that quickly. She is by now so consumed by her own mahaanta that she blames Arjun's & Ovi's unhappiness on her own mahaan self. She has to make amends (not comprehending that Arjun and Ovi are adults and now that they are married, they do not need her interference, sorry, her help, to right their marriage ' Purvi is not their keeper) so she comes rushing to Mumbai to make Onir treat her "sister" who has suddenly grown in stature, not only as Aai's natural born but as Arjun's wife and soon to be mother of her (Purvi's) baby's sibling.
Arjun - the dream of a guy, confident, successful, meets his match in this chit of a girl, falls in love with this novelty, a treat, a delight from mera desh who reminds him of his mom. He will do anything for her, literally anything. He is so much in love that he cannot deny her a thing in the world, even if it is to marry her sister and get her sister pregnant. Come now, he cannot be expected to forget his first love, that is why he is hurt when Onir touches Purvi, he still makes eye contact with Purvi, is concerned about her well-being, once a besotted lover, always a besotted lover. So what if he cares so much for his wife and his own sanity that he is prepared to take his ex-love's baby at her bidding? If Purvi tells him to, he cannot refuse, bechara, he not only gave up his heart to her but his brains as well. And the baby is hers, a great constant reminder of the great love he hath for this girl. He will be forever the benighted lover, only managing to live the semblance of a normal life, happy only because Purvi has dictated him to live the life of a happily married man with wife and child.
Ovi - nothing new about her ever, it is all about her. She wants Arjun, she has Arjun; she wants Purvi out, Purvi leaves Mumbai; she wants Onir in Mumbai to treat her (remember her conversation with Arjun?), Onir comes to Mumbai; she loses baby and Purvi will fall all over herself to hand Ovi hers! Great life to have, to be envied indeed!
Onir - like him and all but he keeps mouthing the same dialogue about what a godh barai means to a pregnant woman (3 times in one epi? really?), being a gyn does not make one an expert on women and their feelings. He is the ideal husband, so in love with his ideal wife and their ideal relationship that he will go to any lengths to preserve their ideal marriage. My sympathies to the poor guy.
Disclaimer : This is the devil's advocate version of the current "lead" characters of the show as Archana has allegedly left (maybe not!) the show and Manav has been made a cameo. No need to dwell on the pavitra rishta pair anymore, thanks to the CVs, all we have left is the new age version of mahaan pyaar, tyagis all around, Purvi sacrificing, Arjun sacrificing, Onir sacrificing and Ovi accepting all their sacrifices like a Goddess (or a child pacified? She looked so like a kid having fun being the center of attention at the godh barai). Good going.