Yakumo Yukari, an old scheming Onmyoji indeed.
As for Mo Yi, he used the Light of the Heart to explain his situation to Reisen. Basically, he had come to help the Princess and was merely infiltrating the crusaders for now, waiting for the right opportunity to act. As for Reisen, she could just go all out. During the fight, he would slack off.
On the surface, however, he righteously declared:
"I never thought this incident would be caused by the Princess—"
"It is fate that has placed us on opposing sides. But Reisen, you need not hold back. Right now, I am merely an enemy standing in your way. Give it everything you have and defeat me!"
Upon hearing that, Marisa patted Mo Yi on the shoulder with great admiration. "Mo Yi, you really didn't disappoint me!"
After giving it some thought, Mo Yi decided to have Reimu, Marisa, and the others go on ahead while the rest of them stayed behind to cover their retreat and have an evenly matched battle with Reisen.
Of course, the real reason was that Mo Yi felt it would be too much for Reisen alone to deal with Hakurei Reimu, Yakumo Yukari, Marisa, and Patchouli at the same time.
At the end of the day, Reisen was only a veteran of the Moon War. Even if she was the king of soldiers, so what? This was not the set of an urban novel. Reisen did not have the ability to give an order and summon a hundred thousand Moon War veterans, each of whom could slap Yakumo Yukari once.
Soldiers were soldiers—mere consumables. Even if they became stronger under Yagokoro Eirin's guidance, they still had the limitations of mass-produced products.
Most worlds with supernatural powers were all about bloodlines, especially 2D worlds. Take