sg starop has my heart. i honestly like it so much more than sg megastar, bc you still have the toxicity, but it's also a cross-faction thing.
ESPECIALLY when starop are bitter exes with a long history. starscream meeting orion pax back at the academy, when he was a scientist and orion was a clerk. the two of them hitting it off instantly. starscream finds orion to be one of the few who does not belittle him for his craft, and orion thinks the seeker is as clever as he is beautiful, making for wonderful company in an otherwise maudlin existence.
and their opinions mostly align, with both of them having issues with the current corruption on cybertron. but while starscream wants reform, orion wants power and control. he decides to gain infamy and influence through politics, and changes his name to optronix, which he feels is more imposing. starscream disapproves and still calls him orion in private, but nonetheless helps him in his campaign.
and it works. optronix gains allies, whether through subtle power plays of his own that starscream helps plan (with much heasitancy) or through blatant threats and extortion (that he never tells the seeker about). starscream is growing far more worried with the twisted person orion is becoming, and of the mechs he's surrounding himself with. Notoriously calculating Prowl, the ruthless Jazz, the mad doctor, Ratchet, and worst of all, the treacherous advisor, Alpha Trion. but telling orion as such is met with calm reassurances and sweetened promises that everything was completely fine. wanting to trust the mech he loves, starscream accepts them all, and swallows his complaints.
until orion finds the matrix. he listens to alpha trion's twisted words and locates the mystical object deep below the caverns in iacon. the matrix, nothing more than a conduit that grants the bearer the blessings of an evil god, corrupts what is left of orion's good nature. the mech emerges from the caves, calling himself optimus prime, and promptly launches a coup against the current high council, backed by his numerous supporters. he kills the senate and sentinel, the blackened false prime, with his own servos. he orders his followers to hang them in the streets for all to see, before leaving to see his seeker and tell him of the news.
starscream, completely unaware, is horrified when his beloved marches into their shared quarters, covered in energon and declaring himself the ruler of cybertron. the new prime explains what he has done, sparing no gruesome detail, and his plans for a cybtertronian empire that spans the universe. the seeker hears optimus's words and sees only a future of endless tyranny, where millions suffer for the sake of a madmech's megalomania. for the first time, starscream sees the mad glint in optimus's optics and wonders if the mech in front of him is still the same one he fell in love with.
optimus holds out a servo and asks starscream to join him, to rule the planet by his side. the seeker slaps his hand away in disgust, denouncing all of optimus's grand plans, declaring him no better than the council he had just overthrown. this is not what they wanted, starscream argues, and certainly not what he had signed up for. he pushes the new prime off to the side, and moves to leave. for good.
but optimus is furious. he drags starscream out of their room and puts him in chains, forcing him to watch as the newly-dubbed Autobots burn down his home, Crystal City. optimus is indifferent to the seeker pleas for mercy, and instead has him transported to iacon, where starscream is posed to remain for the rest of his existence.
optimus is confident he can get starscream's walls to fall, and convince his lover into joining his side. optimus still loves him fiercely, still wants him by his side when the prime ushers in a new era. there was no other mech like starscream on the planet, and optimus refused to share him with anyone. the seeker would be his, forever, whether he liked it or not.
but it does not happen. the convoy is attacked on the way to iacon, by the newly formed revolutionary group, the decepticons, and their leader, megatron. starscream is taken. at first for ransom, but then the seeker joins the group, hoping to bring down optimus's regime and return his once-love to the right side.
when the transport vessel arrives, damaged and empty, optimus is besides himself with rage. he kills the useless guards on the spot, and declares open war on the decepticons. he vows to get his seeker back, to tie him to his berth and clip his wings, to love him so fiercely and fully he never knows anything but optimus and never again has the strength to run away.
but when next he sees starscream, it's with bright red decepticon insignias on his wings. optimus sees starscream’s smile and his happiness with the members of his new faction, and goes mad with jealousy. and thus begins optimus's hatred of all decepticons for corrupting his beloved, and his obsession with getting starscream back.