(I couldn't think who would genocide so I went with Chara. And it's gonna be a long fight so be ready to read a long, Undertale garbage chapter. And yes, this is how much hell a fight with Tara is.)
Chara: *walks down the hall*
*Tara is waiting for Chara, with a few of her family's belongings hanging out of her shoulder bag*
(I just realized Tara rhymes with Chara :P)
Tara: You made it. I guess now you think you must be pretty powerful, huh?
Chara: I am.
Tara: Then isn't it your responsibility to use it for good, and not this disaster...?
Chara: Yes.
Tara: Very well. *left eye becomes purple* Why did you kill my family?!
*battle begins*
Tara: MY MOTHER, FRISK?! *shoots 40 dagger-like magic stuff at Chara*
Chara: !! *runs to the side avoiding*
Tara: MY FATHER, SANS?! *aims 20 Gaster blasters and shoots them all at the same time*
Chara: *dodges somehow* *uses Item* *Hp maxed out*
Tara: MY UNCLE, PAPYRUS?! *shoots 30 more daggers*
Chara: *gets hit but is still going*
Tara: MY AUNT METTATON?!! *surrounds Chara with Gaster blasters and shoots them all at the same time*
Chara: *still has 60 hp*
Tara: And my cousin, Max?!! *blasts all she got at Chara*
Chara: *runs around avoiding everything*
Chara: *clicks Fight, gets it exactly in the center*
Tara: *teleports behind Chara*
Chara: !!! *tries to stab her*
Tara: *grabs Chara's hand* *shoots 5 Gaster blasters at Chara*
Chara: *still has 50 hp*
Tara: If you survive this, you will have to get through my special attack.
*a bunch of Gaster blasters appear to surround Chara*
*daggers appear around the Gaster blasters forming a ring around Chara*
Tara: Get. *Gaster blasters are ready to shoot*
Tara: Dunked. *daggers move backward to build up speed*
Tara: ON. *all daggers and Gaster blasters attack Chara*
Chara: *still has 20 hp*
Tara: You're pretty strong, aren't you, huh? Well then. *purple soul glows*
Chara: ?!
*Tara becomes just like Ultra Sans (fanmade hell where there is no possibility of winning unless Annoying Dog saves you)*
Ultra Tara: Try aNd geT out of tHis, yOu MegalOmaNiac. *Omega Flowey's laugh*
Chara: Shit
Ultra Tara: This iS foR Mom! *blasts ten beams at Chara*
Chara: *somehow stays alive* *is about to click Fight*
Ultra Tara: *punches the Fight button, breaking it the same way Asgore breaks the Mercy button*
Ultra Tara: ThiS is fOr mY daD! *blasts 50 beams at Chara*
Chara: *somehow dodges* *tries to use item*
Ultra Tara: *grabs the Item button* *breaks it in half* We doN't lIkE cHeAteRs, dO we? This iS for my uNcle... *shoots beams*
Chara: *somehow avoids them* *is about to click Mercy to flee*
Ultra Tara: *blasts at the Mercy button* ah-Ah-aH. No fLeEiNg fRoM Me. *grabs Chara* tHis Is foR my aUnt... *blasts her with everything she's got*
Chara: *closes eyes* *still has 10 hp*
Ultra Tara: aNd tHis iS fOr Max. *blasts her with five beams*
Chara: *dies*
*Ultra Tara returns to normal form and looks blankly Chara's dead body*
Tara: Get dunked on, you family murderer.
(Alternate ending)
Tara: You must feel pretty powerful, huh?
Chara: No.
Tara: Of course. You still need to get rid of me and King Asriel. I already know you're already pretty powerful, lvl19 is...hard to believe. But isn't it your responsibility to use it for good, and not this disaster...?
(Yes, I said King Asriel because this is sorta the second generation so yeah :P)
Chara: No.
Tara: I understand. *left eye becomes purple* You brutal slaughterer...!
*battle begins*
Tara: WHY DID YOU KILL THEM?!! *aims 10 purple skulls, 20 Gaster blasters, 40 daggers and 60 purple flaming heart-shaped stuff at Chara*
Chara: shit
Tara: WHAT HAVE THEY EVER DONE TO YOU?!! *makes them all attack Chara*
Chara: *still has 65 hp*
Tara: WHAT DID THEY DO TO YOU SO YOU CAN RUN AROUND MURDERING LIKE THEY'RE ANIMALS IN A SLAUGHTERHOUSE?!! *makes 10 skulls attack Chara*
Chara: *60 hp* *clicks Fight and gets it in the exact center*
Tara: *teleports to behind Chara* Don't even think about trying to kill me. You have no chance against me. *makes Chara's "soul" purple*
Chara: Don't try and do what your father once did to-
Tara: *makes her slam against the floor hard* *slams her onnthe floor until she dies*
Tara: Get dunked on. *walks away from Chara's dead body* Dad, I hope you're somehow proud. I've avenged you all. *teleports away like it never happened*