The main reason for the opposition to Naosuke was his signing of a treaty to open trade with the United States after U.S. Commodore Perry opened up Japan with the threat of force. Shoin, who was a samurai intellectual from Hagi, opposed the treaty with the United States. For this, Naosuke had Shoin executed.
The article states that the Hikone municipal government is holding a series of events commemorating the 150th anniversary of Naosuke's efforts to open Japan to the rest of the world including the promotion of friendship between Hikone and Hagi by expressing its condolences over the death of Shoin.
What is interesting is that Hikone is holding these events in order to rehabilitate the image of Naosuke from that of a brutal dictator. Interesting because the many books I have read about this time period have explained pretty clearly what a brutal dictator Naosuke was.
However, Hikone's attempts to rehab Naosuke's image may not be that inappropriate. Clearly his tactics for achieving his goals were extreme and brutal. But today there is little debate that Naosuke's attempts to open the country were necessary and far sighted. He was pragmatic and knew that Japan needed to open up to the rest of the world and to modernize if they were to avoid foreign domination at the hands of the Americans and other western powers.
Although Naosuke's purge was successful in silencing his high ranking samurai opponents, it did not have the same effect on the lower samurai. In March of 1860, Naosuke was attacked by a band of 17 young samurai loyalists from the Mito Domain and cut down in front of one of the gates of the Shogun's Edo castle.
Naosuke's murder crushed any hope of the resurgence of power to the dying Tokugawa shogunate. His death led to eight years of loyalist samurai terrorism across Japan and the restoration of rule to the Emperor in 1868.