(Sign explaining legend of grave of Jesus Christ, in Japanese.)
“Leo Quix” has an interesting post today, Parahistory and the Historical Jesus:
In 1935, while researching his family’s library in the prefecture of Ibaraki (about 60 miles northeast of Tokyo), a man named Kyomaro Takeuchi claimed to have unearthed some very ancient documents which turn out to be the source of this peculiar, lesser-known variant of the Jesus legend. [me: does this sound familiar?] These documents included the Legend of Daitenku Taro Jurai (the Japanese name that Jesus would reportedly take on for himself). The legend revealed that Jesus first came to Japan during the reign of the eleventh emperor Suinin, landing at the port of Hashidate (on the western coast of Honshu), and that he eventually settled in the Etchu province, where he studied Japanese language, literature, and philosophy under a Shinto priest.
After this formative period of immersion into pre-classical Japanese culture, it is reported that Jesus returned to Judea. The New Testament tells us what happened next. The part where Jesus less-than-triumphantly marches into Jerusalem one Passover weekend to usher in the new Davidic age, botches it up and then proceeds to get crucified in the process for all his trouble, is ingrained into our collective cultural frontal lobe. There’s no need to revisit the details of the familiar story. But the Takeuchi documents have a different, happier ending than the New Testament does. They inform us that Jesus was in fact spared the undignified death outlined in the gospels. Cancel the passion. Cancel the resurrection. Cancel Pentecost. The ancient texts tell us that Isukiri, Jesus’ baby brother, voluntarily took his place and died instead. Having thus escaped death by the hand of Rome Jesus hurried eastward, carrying with him his martyred brother’s ear and a lock of hair from their mother. After much hardship along the long way from Judea to Japan (via Siberia and Alaska—!!—, we are told) Jesus eventually made it home to Japan. The legend then holds that during this second visit, Jesus eventually settled down in Herai, married a woman named Miyuko, worked as a simple rice farmer, raised a couple of daughters, and later died there at an extremely advanced age. The Takeuchi documents further reveal the Sawaguchi family to be the direct descendants of Jesus of Nazareth
The tale of Jesus being swapped by a doppelganger is at least as old as the late 1st / early 2nd century. The first person to have promulgated this variant of the myth is a Gnostic named Basilides, who was said to be a disciple of Peter. In Basilides’ version, Jesus switches places with Simon of Cyrene and looks on while Simon is crucified. I’m not sure whether Basilides was a true docetist or not, but docetism might be at play there.
Of course, you may think that the tale ends there, but the same motif seems to have been involved in the foundation of Islam. In Islamic lore, Jesus is switch by Allah himself with a sort of ghost or phantom (i.e. docetism!) on the cross. The phantom is “crucified” while Allah whisks the real Jesus up to heaven. Literally, the Koran says that it only “seemed” that Jesus was crucified but actually wasn’t; and that’s exactly where the word “docetism” comes from: Dokeo (δοκέω), “to seem”.
He also has this footnote at  about the strange name of the brother who is crucified in Jesus’ stead:
The phonetic quality of written Japanese katakana highlights a curious relation between the names of the two brothers. The name of Jesus, イエスキリスト (= Iesukirisuto) contains the name of his brother イスキリ (=Isukiri). It’s really a condensation of the first five characters of the former name to four (just omit the ‘e’=エ). Compositionally, this link between the names sets up a potential doppelganger motif to the tale. Note that the name Isukiri is a far cry from Jacob, Judas, Simon, or Joses, the names of Jesus’ brothers as listed in the Gospel of Mark.
This is interesting because one of Jesus’ disciples is named Judas “Twin Twin”. That is, Judas Didymus Thomas. Didymus (δίδυμος) is Greek for “twin” and Thomas is Aramaic for “twin”.