They are probably extras, (they will drop nothing till the chapter in which they are first used) when you get to chapter that uses them you will be asked to do a dragon dance adventure. The reward for that adventure is 2 trees ( be sure to look in inventory after each adventure for the prizes) Keep doing dragon adventures in the first few days without doing upgrade till new chapter is about due to start. If you upgrade too soon your collections from event items will not yield anything, similarly adventures will disappear from the list until next chapter.
If you look and read page one of this thread most of this information is there, then read a few of the posts by players and you may find all of your questions answered there.