Otenmon no Hen (The Otenmon Gate Incident) (応天門の変)

The "Otenmon no Hen" (the Otenmon gate incident) was a political incident which happened in 866, in the early Heian period.

The Otenmon gate was set on fire, and TOMO no Yoshio, the Dainagon (chief councilor of state), accused a noble MINAMOTO no Makoto, the Sadaijin (minister of the left), of committing arson. However, FUJIWARA no Yoshifusa, the Daijo-daijin (Grand minister of state), provided counsel and Genshin was set free. Later on, TOMO no Yoshio and his son fell under suspicion as the result of a tip from an informant, they were later convicted and faced banishment. This incident brought the notable Tomo clan (the Otomo clan), which had lasted since ancient times, to ruin. This is considered to be one of the affairs in which exclusionary practices were used against other clans by the Fujiwara clan.

The Course of the Incident
TOMO no Yoshio, the Dainagon (chief councilor of state), was on bad terms with MINAMOTO no Makoto, the Sadaijin (minister of the left). It is said Yoshio wanted to become the Udaijin (minister of the right), by bringing down MINAMOTO no Makoto. That would make the Sadaijin position vacant so that Udaijin FUJIWARA no Yoshimi could fill the role.

In 864, TOMO no Yoshio tried to make a federal case based on the rumour of rebellion by MINAMOTO no Makoto, but this did not get taken up.

In April 28, 866, an incident occurred in which Otenmon gate was set alight and destroyed. The Imperial Court was in an uproar, and many people performed incantations and prayers. Soon after, TOMO no Yoshio claimed to Udaijin, FUJIWARA no Yoshimi that MINAMOTO no Makoto was the perpetrator of the crime. The Otenmon gate was built by the Otomo clan (the Tomo clan), so he said MINAMOTO no Makoto cursed the Tomo clan and set fire to it.

FUJIWARA no Yoshimi ordered the arrest of MINAMOTO no Makoto, and so soldiers were sent and his house besieged. Members of the house of MINAMOTO no Makoto, the Sadaijin, who were accused of the crime, were devastated and distressed.

When FUJIWARA no Mototsune, the Sangi (government adviser) mentioned this to his father, FUJIWARA no Yoshifusa, the Taisei Daijin, the surprised Yoshifusa went before the Emperor Seiwa and defended MINAMOTO no Makoto. MINAMOTO no Makoto was set free, and the soldiers who had besieged his house were withdrawn.

On August 3, OYAKE no Takatori, the Gon no shisho (an assistant doing miscellaneous duties about documents) of Bicchu Province, came forth claiming that the arsonists of Otenmon gate were TOMO no Yoshio and his son TOMO no Nakatsune. Takatori claimed that he saw Yoshio, Nakatsune, and Toyokiyo, the Zoshiki (low-level functionary) run away from the front of the Otenmon gate, which went up in flames directly after. It is said that Takatori held Yoshio responsible for his children being killed by Yoshio's attendant male servant, IKUE no Tsuneyama.
(Another theory is that Takatori blamed Yoshio because Takatori's child argued with a child of Yoshio's treasurer who then punched Takatori's child almost till death.)
Takatori was handed over to the kebiishi (office of police and judicial chief).

The Emperor issued an Imperial edict and ordered an investigation of TOMO no Yoshio. TOMO no Yoshio, TOMO no Nakatsune, IKUE no Tsuneyama, and TOMO no Kiyotada were arrested and interrogated (possibly tortured by continuous whipping), however, they denied having committed the crime.

On September 22, the court found TOMO no Yoshio and others guilty of the arson of the Otenmon gate, and their punishment was banishment, rather than the death penalty or that of a first degree crime. TOMO no Yoshio was sent to Izu Province, TOMO no Nakatsune to Oki Province, KI no Toyoki to Awa Province, TOMO no Akimi to Iki Province, TOMO no Kiyotada to Sado Province, and KI no Natsui and others who were implicated were also punished. Also, FUJIWARA no Yoshifusa ended up gaining total control over of the court due to the sudden deaths of both the ministers of the right and left, MINAMOTO no Makoto and FUJIWARA no Yoshimi, not long after this disciplinary action was carried out.

FUJIWARA no Yoshifusa, who dealt with this incident, ostracized proponent officials of the Tomo clan and the Ki clan, and succeeded in expanding the Fujiwara clan's power by becoming the regent of the Emperor Seiwa after the incident.

This incident was also painted in the National Treasure 'Ban Dainagon Ekotoba' (The Tale of Great Minister Ban).