It's another arc about false pride, isn't it? If he just did as the Tokugawa wanted, everything would work out. But, no, he's got his genius vision, blabla. Now he's going to die. Congratulations, dude#5623 who thought he was above the rule.
Also, come on, send some soldiers to "escort" the psycho dude. Don't just let them walk around doing whatever. Just in case.