I'm a frequent korean drama/movie watcher and i see this all the time: couples celebrating their 100th day together.
I am in the beginning stages of a relationship with a Korean boy myself, so my curiosity about this subject has grown. I thought it would be a neat subject for a culture class, maybe explaining where this comes from (if there is any clear origin), things that couples usually do together, places they go, types of gifts (i've heard couples rings are a very popular 100th day gift?), ect.
I apologize if this has already been covered, I looked around but didn't find anything on it.