Yun-lee is a girl who is carrying a huge emotional scar in her heart. Due to an accident, she lost 2 precious years of her life, the time period between 19 and 21 years old. Her life is empty. She is miserable, but still attending a preparatory school in an attempt to catch up with all the time she has lost. Suddenly, one day on her way to feed some stray cats, she comes across a young man who seems to have what she has lost... the period between 19 and 21 years old.
The quality of manga readers can vary. The uploads are often done cheaply or as a serious hobby by a collective. Be aware that sometimes licence hasn't been given but the sites noted above, Manga Fox in particular, are extremely careful about adding and pulling mangas according to license agreements. So you shouldn't have to worry too much about the material being pirated. There are also translated works and non-translated. Amongst the translated works you will find that the quality of translation may vary according to the skills of the translators. Usually the works are perfectly readable anyway, with only a few added or dropped words or a word in the incorrect tense or with/out plurals. But sometimes the text becomes gobbledygook. In which case, either seek another version or give up and buy an official copy once a printed translation comes out. The other issue of note is you may need to expand the screen to read the text easily as sometimes the scans are minimised a little.
I find that if a page doesn't download properly or some other issue occurs (too slow or someone ordered the pages incorrectly etc.) with one reader then skipping across to another reader and picking up where I was is quite easy and rarely annoying.
Otherwise, enjoy and watch out you don't get too addicted you forget about the necessary things in life.