As the book’s title suggests, this volume deals with the advancement to Underlord, though for more than just Lindon, Yerrin, and Mercy.
The Tournament is coming up and the Akura clan wants new Underlords to compete in it, to that end the Akura’s training ground is opened and chaos ensues.
SPOILERS BELOW
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Because Spiritual Beasts advance differently, Orthos feels it is time to go. Blessedly, we see him again in the Epilogue where he has come to Sacred Valley to check on/save Lindon’s sister.
Yerrin gets into a spat with the other team (from the Seishen) which damages her Vital Aura, normally a fatal wound, but she was already planning to advance to Underlady so not a big deal, as long as she gets on with her advancement, which she does in the end.
We find out about Mercy and what’s going on with her involves a bet. She loses the bet, and gets her power restored, though she will be leaving the Blackflame Empire to train for the tournament.
Lindon advances and reforges his arm (using the Archstone, no less!). For leaving Harmony to die, he is forced to join the Akura’s team for the tournament, which means he and Yerrin will be on opposite sides.
I like that Under-person requires stating the truth of why you practice the sacred arts. For Lindon it is so he “won’t be worthless anymore”, while Yerrin practices because she doesn’t want to hurt anymore. Mercy is so her mom will be proud of her.