Both stories are set at school. The character of main leads also quite similar. The female leads are very shy and quiet girl, but Komi-san is more quiet than Sawako. The male leads support the female leads to socialize and communicate better with people around them. I hope more dramas can be made just like these two.

The story maybe different between these two, but both main leads have pretty similar character. Both female leads are very shy and kind hearted girl, and both male leads are also kind and caring person. Very cute and fluffy couples.

Both dramas are about love after marriage and their relationships develop very well and so sweet.

The differences are the character of main leads. In 'Once We Get Married', the male lead is a rich CEO and a cold man against anyone until he falls in love. While in 'Marry Me!', the male lead is an ordinary employee, warm and caring person.
The female lead in OWGM is talkative and communicate well with people around her, while in MM! the female lead is very shy and doesn't talk too much but very kind and warm.

Both female lead are so nice, warm and kind like an angel. But the FL in Koe Koi is a little bit more shy with the ML than the other one.