Kara, Winn and James were summoned to Cat Grant's office fifteen minutes ago. When they entered the room she ordered the three of them to sit down on one couch, while she herself sat down on the other one. After a very awkward silence and being cut off every time one of them tried to open their mouth, they listen to Ms. Grant berating them for letting James be the guardian, especially since he's so recognisable, for about ten minutes. When all out of sudden Ms. Grant falls silent before saying "Clark" in a very flirty tone. Even after all these years of Clark being with Lois, she still hasn't given up on trying to win him over.
Clark completely ignores her and walks over to Kara, surprising the others. He stops in front of Kara before punching her in the cheek and sending her flying. Kara lands in front Ms. Grant's desk "Clark?" she asks confused by what her cousin just did. The Catco employees who heard the sound Kara made when she landed gather in front of the glass doors of Ms. Grant's office, curious about the sound they just heard.
Instead of giving an explanation about what he just did, Clark stalks towards Kara "This is my planet" he grabs Kara by her arms and lifts her from the ground before continuing "These are my people" Clark throws Kara through the glass doors shattering them. Everyone, except for Winn, James and Ms. Grant (who already had a strong suspicion that Kara is Supergirl), is shocked to see that there's not a single scratch on the reporter, whom they nicknamed Sunny Danvers, after flying through glass. Clark walks through where previously the doors were which he just shattered with Kara's 'help' "And I will not let you harm them"
Kara jumps back on her feet and uses her super speed to close the distance between her and Clark before pushing him and sending him flying. She no longer cares about keeping her identity a secret, the most important thing is to stop her cousin from hurting the people around them on accident. Just when Clark is back on his feet the whole floor is filled with a bright light, stopping the fight between the two famous cousins momentarily. When the light has faded Rhea is standing there. Kara immediately demands to know "What did you do to him?"
Rhea doesn't blink an eye as she answers "I once told you that my planet was riddled with the corpses of yours, but not only green kryptonite rained down from the skies, there are so many other ways to harm your kind and to simply weaken you. Silver kryptonite. Your cousin is so much like you, reckless, stupid, heading head first into danger. I couldn't have set a better trap if I tried. I only had to give him some intel for him to fly here to end you and expose his real identity"
Kara tries to get Clark to recognise her "Kal, it's me, Kara"
However, Rhea smiles a little at Kara's attempt and she informs Kara "Oh, I wouldn't even bother. He doesn't see you, he sees his worst enemy"
Clark immediately confirms this by saying "You should have stayed away, Zod"
Kara can't get herself to stop trying to diffuse this situation without fighting the very person she's supposed to protect "Kal, listen to me-" but she's cut off by Clark using his heat vision on her. Kara responds by using her own heat vision and they walk in a circle. All of the employees are still watching, too dumbstruck by the revelations made and in awe of seeing the two Superheroes in the same room, to grab their phones or move in general. They can't believe that their own reporter Kara Danvers is Supergirl, that the most well-known Daily Planet reporter Clark Kent is Superman and that they're fighting one another.
Rhea starts talking again, amused by the sight of the two cousins "You're his mortal enemy, Supergirl. The person he fears most, you'll take everything of him so this time he won't hesitate. This time he will protect his planet. This time-"
Clark interrupts Rhea to finish the sentence she started "-I'll stop you forever" and he charges at Kara. They both crash through the window.
They fight while being in the air trading punches and kicks before crashing into Lena Luthor's office.
Clark grabs a large piece of cement and throws it without looking. Kara moves in front of Lena quickly to prevent her from getting hit and hurt. Unlike many others, Lena's not really surprised by the revelation of the two identities. She already knew Clark Kent is Superman because of her brother and she figured out on her own that Kara Danvers is Supergirl.
As soon as the cement is broken, Clark moves forward "Stay away from her" he says before he throws Kara out of the window and he follows her. They hit the ground multiple times before finding themselves inside Catco again. Both of them have lost their glasses and their superhero suits have become partly visible through the tears in their clothing.
It's visible that both Supers are getting tired, nevertheless, the fight continues and Clark pushes Kara against the wall. Kara frees herself and they exchange blow after blow, without anyone seeming to win. They fly around the floor breaking several desks, chairs and other furniture and decorations. After a minute they both land and they use their heat vision again. When they move both of their heat vision miss their target and start small fires, which they immediately put out with their freeze breath.
When they're focused on each other again, Kara delivers an uppercut to Clark's chin. She quickly swings her arm again, but Clark ducks and she misses. However, she receives a direct hit in the face as a thank you. Clark tries to hit her again, Kara blocks him and delivers a punch on Clark. They both stumble, Clark from the impact and Kara because of the power she put behind it, being very eager to let the fight stop as soon as possible. Clark charges at Kara again, throwing an uppercut that Kara easily avoids, but he's able to grab one of her arms and he holds Kara against his body securing her right arm with one hand and pressing his other hand against her collarbone. Kara waits a few seconds until Clark relaxes a bit before hitting him in the ribs using her left elbow, forcing him to let go of her.
The people in the office are still following the fight closely and they hope that whoever is in the right state of mind, and they concluded that that is most likely Supergirl, will win
While Clark lets her go, she grabs his arm and twists it behind his back "You have to fight it" she yells desperately before being punched in the stomach and having to take a few steps back. As Kara is trying to regain her breath, Clark sends her flying into a wall. He speeds towards her and kicks her in the stomach again letting her fly a few feet back to the direction she just came from. Just as Kara is back on her feet Clark knocks her down again. Kara is able to stand up quickly this time and she punches Clark sending him stumbling. She follows up with an uppercut and Clark flies against the ceiling before falling on the ground, unmoving. Kara falls to her knees and quickly loses consciousness too.
As soon as both Supers are unmoving, Winn and James go to Superman, while Lena and Alex, who both arrived at Catco just before the fight ended, go to Supergirl. Cat Grant doesn't move towards either of them, but it's obvious that's she's worried about them both. It's deadly quiet in the office during the three minutes it takes for Supergirl to regain consciousness. When she opens her eyes she stands up and she stumbles over to Alex and then Superman before taking off while carrying both.
"Not a single word about what just happened gets out. If anyone reveals the secret identities of Superman and Supergirl you won't live long enough to see it reach other people. Also, anyone who treats Kiera differently after today is fired and I'll make sure you'll never have a job again. Understood?" Ms. Grant half tells and half threatens everyone in the room, setting the example by mispronouncing Kara's name. Although she threatened to fire Kara when she first suspected Kara was Supergirl, she's beginning to understand why Kara's day job at Catco means so much to her. Being away has made her realize quite a few things that will help her in the future. For now, she sees it as her job to make sure that Kara Danvers and Clark Kent can continue to live a sort of normal life in peace, not knowing that before the end of the day no-one will remember seeing the secret identities of Superman and Supergirl being revealed, courtesy of J'onn J'onzz.
If you have some time, I would love to hear what you think