Unmei ni, Nita Koi

I know big age gaps can be uncomfortable for some people, and they don’t like watching K-Dramas with couples that have big age gaps from one another. Because of that, they’ll miss the chance to see that the couple actually does have spectacular chemistry and that their age gaps aren’t noticeable!

This is a love story about Ogawa Manami, a high school teacher who grew up in a strict family, and Kaworu, a host who is not good at reading and writing, as they search for love despite the obstacles they face. Manami is being pressured to marry a man she met through her father's introduction, and the high school where she works is also facing a crisis of class collapse. She spends her days lamenting, "I want to run away from this place." One day, she receives a call saying that a student has been deceived by an unscrupulous host, and she rushes to the store to bring the female student back, where she meets Kaworu. Kaworu has to sign a promissory note promising not to contact the student in the future, and Manami finds out about the problem that he had kept secret from anyone until then. In the play, the two gradually become closer through Manami's secret "private lessons," in which she teaches Kaworu about language and society.

Glass no le and Unmei ni, Nita Koi have a very similar feel to them. Both featuring Saito Takumi as the main male lead with mature and realistic romances.

Both have a rich male celebrity meeting the relatively poorer FL again after many years. In Radio Romance the ML is in entertainment business where as the other the Ml is a famours designer.

45-year-old Rui Nakamura (Kyoka Suzuki) is a highly successful publisher. During the course of work, she encounters a 28-year-old married man named Kou Suzuki (Hiroki Hasegawa) who aggressively pursues her. Unexpectedly, Rui Nakamura starts to fall in love with the younger married man

Saito looks great here

It's romantic, but riddled with the heartwringing conflict that makes you yearn for a happy ending (I hope we get one). The actress playing the romantic female lead (the destined one) is very good.
the story is about Kasumi (Tomoyo Harada) is divorced and lives with her high school student aged son. She supports her family by delivering laundry. One day, she meets Yuri (Takumi Saito). Yuri is a customer of the laundry delivery service. He is a popular designer, known for his designs of cafes and furniture. Yuri talks to Kasumi without restraint. At first, Kasumi is cautious around him, but she becomes attracted to him.