Who is this mystery girl with blue hair?
The fact is, we don't have a clue from the series. Our best guess is the Livlaster.

Reason 1 - They were confirmed to be living things with a will, but we never really "met" them. We met the machines, but not them, which is odd.

Reason 2 - Her color style is the same as Daichi's Livlaster, so there is reasonable evidence to make the connection.

Reason 3 - She was first seen when he got the Livlaster. She is only seen with Daichi during critical moments for him. So she and he are connected.

The next best option is Pitz, but we never gave a corresponding figure for the other squirrel. However, this is probably the second best theory based on the evidence. Following that theory is a new character (like a planetary gear) to intro into a season 2. We have no reason to suspect this, but hey, we don't know. Lastly is Daichi's mom. He lives with his uncle, his dad died, so we have a missing mom figure. Maybe there's some backstory?