Based on the song made of love by the show STEVEN UNIVERSE (it's not the exact thing, but just imagine it)

This is Frisk, back to get her,
And we'll never go down not ever Because me and Sans are stronger than you,
We're stronger the both of us two,
You may think you'll win the fight,
But we have determination through the night,

Sans is my fury, I am his lover, we are our inspiration, we-e-e have,
De-etermined love, de-etermined love, de-etermined love, and we're stronger than you,
De-etermined love, de-etermined love, de-etermined love, and we're stronger than two,
De-etermined love, de-etermined love, de-etermined love, and we'll be as strong as you,
De-etermined love, de-etermined love, de-etermined love, and we're stronger than you,

This is who we are, this is who I am, I won't you hurt my feelings, I won't let you hurt my friends,
So go ahead and try to kill me if you able, can't you see our determination is stable,
Chara you can't even hit me, because you know that you can't even see me,
We are more than just two unlikely friends,
We will stick together to the end,

So why don't you join us, why don't you see, we can be friends yeah you and me, beca-ause we have,
De-etermined love, de-etermined love, de-etermined love, and it's stronger than you,
De-etermined love, de-etermined love, de-etermined love, it's as strong as us two,
De-etermined love, de-etermined love, de-etermined love, and it's for me and you,
De-etermined love, de-etermined love, de-etermined love, and we promise to spare you,
~SONG ENDS~

FRISK: so, what do you say, will you be determined with us Chara? *Holds out hand*
SANS: we could use another friend on our team. *Smiles*
     (Sans and Frisk are sparing you)
CHARA: But, I don't get it. I killed everyone, and yet you still want to spare me?
SANS: we are forgiving you.
FRISK: you may do horrible things, but Chara, you're still a part of us.
CHARA: *stares at Frisk's hand* ... Ok. I'll be determined. *Grabs her hand*
The end......