The biggest issue I see with this series is that, the complete lack of any explanation or hint towards the underlying plot of the Series at the beginning. It just jumps into all the events.
I mean, why did Berina suddenly decided to get Tamed by Lint and even help him gather powerful monsters, plus even train him.
She even offered herself in order to be with him, as a proof.
The first time we get some hint towards something going on is after Lint talks about his past on how he got his Tamer class.