Mamahaha no Kokoroe

Misaki Yamazaki passes away due to illness, but when she awakes, she finds that she had been reborn as a character in a manga she had read before her death—the abusive, wicked stepmother of the young protagonist.

Only remembering this the day before her wedding, there is already no way to escape. Determined to treat her stepson well, upon meeting him, she found the boy extremely adorable! As she works to raise the child well with her memories to aid her, the attitude of her cold husband begins to change!?

(Source: Alphapolis, translated)