The original U.S. TV series “CSI (Crime Scene Investigation),” set in Las Vegas, has been so successful that it has almost grown into a franchise, with “CSI: Miami,” “CSI: NY,” and “CSI: Triology.” After visiting the “Ryoma Den” exhibition at the Edo-Tokyo Museum, which looks at the life of the 19th-century samurai and reformer Sakamoto Ryoma, I almost felt as if there had been yet another spinoff — “CSI: Edo Japan”: So much of the exhibition details the grisly circumstances of its subject’s assassination, including a full-scale reconstruction of the actual room in which the deed happened.

But perhaps like James Dean or Che Guevara, the way Sakamoto died is the key to the way he is remembered — and remembered he most certainly is as the subject of NHK’s latest historical drama “Ryoma Den.” In fact, this exhibition is being run in conjunction with that TV series.

Since his death in 1867, at the age of 33, Sakamoto has become a national icon and a symbol of the Meiji revolution that toppled the Tokugawa shogunate and opened the way for Japan’s modernization. This is surprising because, even though he was undoubtedly in the thick of the action, he was essentially a lower-ranking samurai, who died before he could realize his full potential and who never held an important office.

Compared to the likes of Saigo Takamori, the leader of the Satsuma clan forces, or Katsu Kaishu, the founder of Japan’s navy, Sakamoto was a political lightweight and a member of a minor samurai clan. Perhaps the fact that he died so young and was not associated with the main anti-shogunal clans made it easier for him to later emerge as a perfect nonpartisan symbol of Japan’s renewal.

This is the dominant impression that arises from this exhibition: Sakamoto as the ultimate intermediary figure, as someone who could act as a broker between powerful interests — one of his unquestioned achievements was helping to bring the two main anti-shogunal clans, the Choshu and Satsuma, together, despite their long-standing rivalry. But he also seems to stand as an intermediary between the ages, between the feudal Edo Period and the modernizing Meiji Era, which he barely lived to see.

At the start of the exhibition we are greeted by a glass-plate photograph of Sakamoto. The small, monochrome image captures the transitional aspect of its subject. We see an authentic Edo character with all the grit, swagger, and latent menace of the samurai, but, at the same time, the fact that he bothered to pose at all betokens a man with a deep interest in the new ideas from overseas that were transforming Japan.

This also provides a ready comparison with the more airbrushed image of Sakamoto being presented by NHK’s historical drama, which is helping to drive the latest “Ryoma boom.” Another factor is said to be the economic tough times, with Sakamoto symbolizing the manliness and adaptability that modern Japan apparently needs to survive.

The exhibition perhaps suffers a little from this feeling of national self-absorption, and perhaps this is why there is so little English in both the catalog and information plates. This is certainly a drawback to a show in which so much hinges on the many letters and documents on display. These are summarized in Japanese, but the main interest boils down to the calligraphy and who was writing to whom, rather than the actual details that involve wading through hard-to-decipher script, or reading the often vague summaries.

These documents reveal that Sakamoto was a keen correspondent, writing to other important historical figures, friends, relatives (especially his older sister who looked after him following his mother’s death when he was 12) and even, in one case, to the mother of a friend, just to pass on news of her son.

More accessible are the exhibition’s paintings, maps and other items. These include Kiyoo Kawamura’s “Portrait of Katsu Kaishu” (1885), painted in the latest, imported Western style and showing the man whom Sakamoto originally intended to assassinate in 1862 but who managed to talk the young blade around to his own modernizing views.

But what exactly did modernization mean? A number of guns and pistols hint at one element — violence and destabilization. These include the Smith & Wesson pistol that Sakamoto used to defend himself against another assassination attempt a year before his final murder, as well as some British Enfield rifles that he sold to his native Tosa clan a few months before his death.

The most memorable aspect of the exhibition has to be the paraphernalia connected to Sakamoto’s death. These include the reconstruction of the room where he and his companion were sliced to death. You can also see the supposed murder weapons and a decorative folding screen, which was in the room at the time and was splattered with the victims’ blood.

It is here that the CSI part of the show really kicks in. Although mystery still surrounds the murder, the exhibition dares to point the finger at Katsura Hayanosuke, a little-known samurai in the employ of the Kyoto Mimawarigumi police force, which probably means he’s also a likely villain in NHK’s “Ryoma Den.”

“Ryoma Den” at the Edo-Tokyo Museum runs till June 6; admission ¥1,200; open 9:30 a.m.-5:30 p.m. (Sat. till 7:30 p.m.), closed May 24 and 31. For more information, visit www.edo-tokyo-museum.or.jp

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