I'm extremely skeptical that this is true; I'm searching for supporting information on this but am not finding any references in reliable sources (in either English or Japanese).

I'm not suggesting that Ishii never proposed such a plan, but the idea put forward by the referenced TIL post and wiki article that the Japanese were actually planning to implement it in September 1945 only to be stopped by the end of the war stretches credibility to the extreme.

To see why, we only need to look at the supposed means that were going to be used to carry it out. Three I-400-class submarines had been completed by the end of the war: I-400, I-401, and I-402. But I-400 and I-401 had left Japan in late July and were near the Caroline Islands when the war ended. And I-402 had already been converted into a tanker submarine (and was undergoing repairs from an early August air raid when the war ended, in any case). There was one more under construction when the war ended (I-404), but it had been seriously damaged in an air raid in late July. In short, there were only two submarines available to carry out this operation and the Japanese had already dispatched them elsewhere.

ETA: I tracked down one of the wiki article's sources (John Geoghegan's Operation Storm: Japan's Top Secret Submarines and Its Plan to Change the Course of World War II), and it completely contradicts the article's contents. It gives Operation PX as the name of the operation and states that it was killed by the army in March 1945. Searching for "Operation PX" turns up a lot more in the way of information than "Operation Cherry Blossoms at Night" does, including, amusingly enough, another wiki article that completely contradicts the contents of the first.