Yamashita, arrogant, greedy, hot-tempered, and most importantly, he cares deeply about others' opinions of him.
Jiang Kou capitalized on this, prompting him to compete with Xu Renjie.
The match is completely meaningless; if Yamashita had any sense, there'd be no need to wager with medicine. If he truly wanted to teach Old Xu a lesson, he could just call him out and beat him up.
That way, there's no risk of losing, and he could thoroughly mock Old Xu.
Instead of being forced to use every trick due to the rounds, filled with rage as he is now.
Furthermore, Yamashita had never realized that from the moment he agreed to Jiang Kou's proposal, he had already fallen into the trap set by the latter.
It's important to know that Watanabe stated beforehand that tomorrow Old Xu would be going out with Derek to gather supplies.
