I will.keep this relatively short and not focus on the cells because their humour and cuteness just distract from what is a really depressing drama. Yumi is annoying insecure wants the perfect man (they dont exist not even for your cute cells) and as soon as she gets to a point of difficulty in relationship breaks up for selfish and unrealistic reasons. She is annoying. The fact she goes to serial relationship intruder guy in S2 just makes her more unlikeable. The fact she still spends emotion and time on guy1 when in flown blown relationship with guy2 in S2 makes her ...yes even more unlikeable. The fact she breaks up with guy2 mainly because of another woman's interest in him while she has been trotting off to see guy1 througout their relationship makes her again yes...even more unlikeable.
The fact she has to then go to young good looking third guy with no thought for the 2 broken hearts in her wake yes you guessed it makes her even more unlikeable.

People say its not about the romance its all about her and her growth. Well it is totally about the romances through which we clearly see yes it clearly is all about her at least in her mind. As for growth ? All i saw was history repeating itself

Finally why do so many people give this kind of unhappy bad behaviour a pass by assuming it is realistic. None of it is realistic thats why we like dramas, so dramas like this where selfish behaviour is dressed up as realistic slice of life are just a waste IMO. This show turns out to be a pointless story of a woman getting into and ending relationships with nice guys who really like her. Unless you like cartoons and the psychology of a flighty selfish insincere woman who thinks shes always right then there is no real point to it. Sorry it just crystallised that way in my head the more it went on the more the cute funny cartoons couldnt distract from her flawed behaviour. One season would have been more than enough to get the message.