The Light Ray Robot is the 13th episode of the 1980 anime series. In this episode, Astro befriends a stolen invisible robot being misused for crimes.
In late December, The Light Ray Robot debuts at Japan's National Robot Pavilion Exhibition, where he is put on display in the main hall under polarized lights. Light Ray later wins the Robot Art Award, but when his lights are turned on again, he is gone. In the following days, jewellery stores and banks report being robbed by an invisible entity, which some assume is a ghost. At the same time, Skunk Kusai has broken out of jail and is at large.
One morning, Astro's teacher Higeoyaji gets a taunting call from Skunk, who claims to have Light Ray in his possession. Higeoyaji taunts Skunk by calling him a liar, making Skunk angry enough to arrange a secret meeting with Higeoyaji in a public park. Astro happens to fly by and start a fight, enraging Skunk, and causing Light Ray and Astro to fight. That night, Light Ray visits Astro's house, curious about how Astro seems to be inorganic, like himself. Astro takes it upon himself to take Light Ray downtown to teach him how to do good deeds - getting a small boy's hat out of traffic, saving a woman from being accosted by a drunk, and donating clothes to charity - but all are impaired by Light Ray being invisible. Light Ray is heartbroken, and runs back to Skunk's hideout.
The next day is Christmas Eve, and Astro's family is hosting a small Christmas party. Light Ray arrives to the party, and Astro is overjoyed, until Higeoyaji arrives dressed as Santa Claus. He gives Light Ray a necklace with an internal tracking device and spray-paints his legs bright red. Light Ray is horrified to see his "pretty body" painted on and runs away, while Higeoyaji and the police track Light Ray's movements.
Light Ray returns to Skunk's hideout, terrifying the gang as they witness a running pair of red legs. Skunk is appalled, realizing that Light Ray is no longer useful for covert robberies, and his necklace has been tracking his location the whole time. Skunk's men are unable to clean the red paint off, so Skunk constructs a small bomb for Light Ray to take to Higeoyaji's house. Light Ray likes how the ticking of the bomb sounds and decides to keep it for himself.
The police and Higeoyaji soon arrive at Skunk's hideout, and after a skirmish, everyone inside is arrested. Skunk taunts the police by revealing that Light Ray is carrying a powerful bomb, and not even Skunk knows where he is now. A bewildered Light Ray travels through town, while Higeoyaji and the police race against the clock to find him. They police soon discover that Light Ray is walking towards Mount Tsukuba, the location of the Japan National Hospital. The police realize they are unable to get the bomb away from Light Ray, leaving them with two choices: either let him walk towards the hospital, letting the bomb time out and destroy the facility, or shoot him down a fair distance away from it. The police have no choice but to shoot Light Ray with a high-powered beam, which kills him instantly. Astro and Professor Ochanomizu mourn Light Ray at the foot of the mountain.
Canadian dub edit
In the 1985 Canadian version, the entire ending of the episode is changed. Stilled frames and repeated footage are used to replace that of Light Ray's explosion; footage of background shots are used for moments where Light Ray is talking, with the excuse that he is invisible and only implied to be in the shot. In this ending, the bomb malfunctions and doesn't go off. Astro and Ochanomizu (Professor Peabody in this dub) declare this to be a Christmas miracle.