"Bagel Girl" originated in Korea and refers to a sexy woman with a very youthful face.
Bong-gi is an obese and clumsy young man with very low self esteem. He has no friends and does not stand up for himself when mistreated at work. One day he wakes up to find that his body is that of a beautiful and curvy young lady. He has no idea what's going on.
Girl Bong-gi quits her awful job and meets the sister of a former friend. The sister seems well on her way to alcoholism. (FYI, FDA recommends no more than 3 drinks a day 7 drinks a week for women and 14 a week for men.) She concludes that Bong-gi had a sex change and so shows Bong-gi the ropes at being a girl. Those episodes are well done and humorous. It's when the series becomes a murder mystery things go downhill.
It could have been good, but the characters do things that make no sense, just like in a bad slasher movie. No one calls the police, opportunities to fight back or at least struggle are not taken, people announce themselves to the bad guy before attacking which of course leads to failure. Obvious clues are missed or not followed up on. Secrets aren't spoken. I don't want to give it away but in the final 5 or so episodes, people just act stupidly. It got so maddening, I fast forwarded through two episodes. The final episode is OK but it doesn't show what happens with the female lead.
In this series and one titled "Kiss Him, Not Me", the overweight characters are given a weird low somewhat mumbly "fat person" voice. Of course there's no such thing. Overweight people talk like everyone else. I hope this type of voice is left behind.
The animation art is good and you may like it, but I'd recommend the comedy anime "Magical Sempai" instead.