Star in My Mind is the first part of the Star and Sky series. If you are planning on watching Sky in Your Heart, I recommend watching Star in My Mind first to get a bit of background info on the characters. This show is centered around a different couple, but they are from the same universe.
Treasure's first mini web drama. It is sort of a parody of typical high school kdramas, most notably Boys Over Flowers. It is a short watch.
Treasure's second drama. It is about a group of high school students who find out that one of their classmates is a ghost. Follow the boys as they try to figure out who the ghost is!
For new and old fans of Treasure, this youtube show is a great way to learn more about the members and see how they interact off stage.
YGTB is the survival program that formed the group Treasure, so if you are interested in getting to know the boys a bit more, I highly recommend watching.