It's difficult to tell much about "Keyholders' Legacy" without dropping spoilers about the previous series. It's intended as a transition into a story about the second generation of Keyholders.
The new enemy introduced in KL is not from the Gates. This time, the enemy is an organization from Earth that is targeting people who have anything to do with the Gates -- which spells trouble not only for immigrants who have roots in the Gates but also for the Keyholders.
This threat puts the Key-Seekers, an organization that keeps balance and diplomacy between the Gates and Earth, in a risky position. Not wanting to get tangled up in a diplomatic crisis between Earth and the Gates, the Seekers try to cut ties with the Keyholders living on Earth, which only results in more trouble and traps Takumi, a longtime friend of the Keyholders, in the middle of it all.
In the meantime, the Keyholders-in-training become the next targets of this mystery organization from Earth, and several Keys are stolen...
