Suddenly — the February 26 Incident. This blog has written several times about the Takebashi Incident, when Imperial Guards rebelled in the Meiji era, but there is a photograph of Takebashi from the bloodiest event of the Showa era.
It is a precious record kept by The Mainichi Newspapers＝photo top. The date is February 26, 1936. Rebel troops or suppression forces? The rebel units chanting "Showa Restoration" attacked the prime minister's residence, Finance Minister Takahashi Korekiyo's home, and other targets mostly west of the Imperial Palace, occupying the Hibiya to Nagatacho area from bases at the Sanno Hotel in Akasaka and the Army Minister's residence at Miyakezaka. Meanwhile, on the 27th a martial-law order placed the martial-law headquarters at the Army Hall east of the palace (now the Kudan Kaikan — closed after last year's major earthquake)＝photo bottom. Whether rebel troops remained at Takebashi, and until when — or never at all......
I found two accounts that help infer what happened. First, apologies for citing a personal blog, but it is vivid, so I quote it.
"I was a fifth-grader at Nishikanda Elementary School. It was a snowy day. Only a few were in the classroom — or rather, they did not come. Someone said the prime minister had been killed. ... Told school was closed, I went home ... and my brother at Obuta confectionery shop invited me: [Imperial Guards are piling sandbags to defend the palace. Want to go see?] We went to Takebashi. Machine guns were mounted atop the sandbags, and soldiers shouted at us to go home. The air was tense. By evening troops had also arrived toward Surugadai, and we were told to hide behind concrete buildings in case fighting broke out ..." (http://blog.goo.ne.jp/goo2023/e/68944fdba831c689b405f1fece91804b)
From this account, they seem to have been suppression forces defending the palace.
Another source is the Kajima Corporation website, which in an anecdote about the February 26 Incident describes Yamatane Securities founder Tanji Yamazaki.
"(Tanji Yamazaki) learned of the incident shortly after 7 a.m. on February 26 at his newly built home in Kojimachi 3-chome. ... Driving to work, near Takebashi two officers asked him for a ride to the regiment in Akasaka. Coming from Miyakezaka onto the moat road, soldiers stood in line with rifles ready. He reached the office later than usual, but the situation had not yet settled ..." (http://www.kajima.co.jp/gallery/kiseki/kiseki18/kobore18.html)
The Akasaka regiment was probably the 3rd Imperial Guard Infantry Regiment near present-day TBS. Lieutenant Nakahashi Motoaki from that regiment joined the rebels and killed Takahashi Korekiyo, but the regiment's location was near the border between rebel and suppression forces — so from this account alone, it is unclear which side the officers he drove belonged to.
Incidentally, I emailed Kajima's inquiry desk asking why they write about Yamazaki. I received no reply, but I suspect it is because Kajima built Yamatane's headquarters (a new five-story marble building at Kabutocho the previous year), which also appears in the anecdote.
At any rate, civil war was averted — yet the more one reads the records of the time, the more one appreciates Takebashi's peaceful scenery today.