Few problems for me personally is that I can’t suspend my belief when it comes to the magic system in this world. All you need to succeed is to have a decent imagination. Think hard about drawing a cup of water from the river and bam. You can use water magic. What really seems careless of the author is giving the earth element the ability to make precious gems at a very low level. If it was that easy I would think that using diamonds or some other gem would be standard for earth magic.
As far as I understand about the setting is that the nursery raises alien children for mostly military purposes. Maybe? The series waffles on the idea. Kind of contradicts the fluffy image that the author is writing.
As for the story so far, there really has been no interesting characters or plot points. Which is a shame because can you image the type of personalities that find affection or fascination for some of the hulking aliens they call children?
What has happened so far is that the main character has solved every problem by accident or by virtue of being a great person. The Marysue is strong in this series, the main character loses nothing and gets everything!
MC confession to marco seemed to come from nowhere with out much build up.