Anata no Koseki, Ore ni kudasai.

"Ms. Momoko, just like you promised. Please marry me." Momoko Tetsumiya is a 30-year-old cram school teacher with no time for romance, focusing solely on work. "I'm fine all by myself!" Momoko refuses to let anyone or anything interfere with her carefully laid plans for the future. One day, a hot new teacher straight out of the University of Tokyo throws her off her game. Little does she know, he's a former student of hers from 10 years ago. How did her sweet, innocent student transform into this devilishly handsome man? Now an adult and her equal, he's determined to get her to sign a marriage agreement. Can Momoko navigate this unexpected twist in her life?" (Source: MangaPlaza)