My Happy Ending Plan as a Side Character – I Refuse the Villainess’s Bad Ending!

I, Shiho Morimoto, died in a bus submersion accident and was reincarnated into the world of the romance fantasy novel "Cinderella Doesn’t Wear Glass Slippers," which I had read in my previous life. But I wasn’t reborn as a main character or even the villainess — I’m the villainess’s cousin... In the original story, I was the one who triggered the downfall of the twin cousins, Ariel and Eriol, pushing them into darkness. But there’s no way I’ll let things follow the plot this time! To change the fate of this world's me — Selnia, who originally died young — I’ll raise those twins to be kind-hearted children… no matter what!?