Decisive Battle Under the Setting Sun (落日の決闘 Rakujitsu no Kettō) is the thirty-second episode of Return of Ultraman.
MAT was investigating the frequently occurred earthquakes on Mt. Ryujin. Go went on an investigation for Ryujin Tunnel after knowing the accident happened in the tunnel 10 years ago. An earthquake happened again and Go lost his consciousness in a collapse. Monster King Maimai, the cause of earthquakes, appeared and was taken down by MAT! That's what it seemed to be...
Go, Ikeda and Ueno are ordered by Captain Ibuki to investigate the recent cases of earthquakes in Ryujindake while going undercover as tourists to avoid commotion with the villagers. Go visited Sakuta Nohara, a former miner who previously dug the Ryujin Tunnel that supposedly linked from Ryujindake to Tatsunoguchi. As Sakuta recounted, while there was once an earthquake happened due to a cave in during the mining operation, it was due to the soil erosion brought by the heavy rain from the day before the incident.
Meanwhile, Taro Nohara is a troublemaker who has been pulling pranks on the villagers for his own twisted enjoyment, leading to his father getting all the complaints from the victims. A local police named Shigeru managed to drag Taro away from several children and learned that his recent behavior is due to an eavesdropping from a certain conversation. Apparently Taro's real father was Hikota Obayashi, a late miner from Tatsunoguchi of similar age as Sakuta. When the cave-in incident happened, Hikota died and his wife left Taro, forcing Sakuta to raise Hikota's son in honoring his late friend's wish. All these happened when Taro was recently born at that time, bringing tears to both the young boy and the police officer in the present day. AT night, Shigeru and the rest of the MAT members discusses their operation. Unfortunately the crew realized that Ueno is the only one left behind, as he happened to be intoxicated mid-way during the travel.
The next day, MAT members decided to venture into the Ryujin Tunnel, assuming that a monster is behind all the earthquakes and that it would slowly awaken from its slumber. Go decided to enter a small crevice that leads to several stalagmite, but the earthquake quickly trapped him inside. As Ibuki and Oka rode their patrol car, they fail to realize that Taro was hitching a ride on top of the vehicle. The patrol car commences attack on the recently awakened monster. A drunk Ueno was accidentally swatted mid-air but he released a bag full of explosives that instantly amputated the monster's right arm. Although it seemingly stopped its actions, Ibuki is well aware that the monster is still alive.
Taro manages to find and awaken Go in the stalagmite cave. There, they discover the frozen cavader of Tatsunoguchi miners, including Hikota. Go transforms into Jack to get him and Taro out before facing the molted monster. Jack seemingly won by ruining its wings, but the monster quickly countered by spraying cobwebs. After freeing himself, Jack throws his Ultra Bracelet into a timed bomb that finally killed said monster. Taro reconciled with Sakuta and MAT members decided to return home, unaware that they accidentally left Ueno behind.
- Hideki Go (郷 秀樹 Gō Hideki ):Jiro Dan (団 時朗, Dan Jirō )
- Ryu Ibuki (伊吹 竜, Ibuki Ryu ):Negami Atsushi (根上 淳, Negami Atsushi )
- Takeshi Minami (南 猛 Minami Takeshi ):Shunsuke Ikeda (池田 駿介, Ikeda Shunsuke )
- Ippei Ueno (上野 一平, Uneo Ippei ):Hatashi Mitsushi (三井 恒, Mitsushi Hatashi )
- Yuriko Oka (丘 ユリ子, Oka Yuriko ):Mika Katsuragi (桂木美加,Katauragi Mika )
- Fumio Kishida (岸田文夫 Kishida Fumo ):Ken Nishida (西田健, Nishida Ken )
- Ken Sakata (坂田健, Ken Sakata ):Shin Kishida (岸田森, Kishida Shin )
- Jiro Sakata (坂田 次郎, Sakata Jirō ):Kawaguchi Hideki (川口英樹, Hideki Kawaguchi )
- Narrator (ナレーター, NaretaAkira Nagoya (名古屋章, Nagoya Akira ) ):
- King Maimai (Larva and Adult)
- Return of Ultraman Volume 8 Features episodes 29-32.