She has heard of King Sans before.

Frisk hears his name cursed by her father during his rages. (She usually stays out of his way, along with Asriel.) Her twin's cheeks flush whenever she hears his name. All she knows is that people from Ebott run away to enter his kingdom of Snowdin. She has heard that he is a good and just ruler.

The army comes.

Sometimes, she thinks she sees her mother among them. Chara spends most of her time on the battlements. Asgore gives into rages. Asriel is frightened- as the future king, he must spend time in the war room, with their father.

When they lose, Frisk stares at the king.

He glances over Asriel, shivers at Chara, and stared at her. Even as Sans talks to her brother, his gaze always slips to her.

Asriel, now king, asks her to write the peace treaty. "You're better at stuff like this." He explains. Frisk smiled and promises her best. She does as promised and writes her best, and the treaty is good.

Sans seeks her out.

They talk sometimes, his cheeks an odd blue. As the time goes by, Frisk finds her cheeks going red as well.

When Sans shows her the flower, carved so perfectly that she is tempted to smell it, and asks her to marry him, Frisk understands.

As per tradition, the engagement lasts a year. The wedding is a dream come true - her in her mother's altered wedding gown and him in armor. Asriel has a grin, and Chars has tears in her eyes. Sans sets the crown on Frisk's head himself.

Their union is full of love and satisfaction, bearing one child.