The Machiners are a race of machines who live on Earth unnoticed by humankind. They have their major appearance in the corresponding story arc (from chapter 174 to 176.)
When they first arrive at Whirlwind looking for Belldandy, the machiners are searching for someone to repair them, but Heaven's magical programs do not affect them very well if at all. Keiichi offers his help and becomes very fond of these mechanical creatures. When it comes to rescue one of the flying machiners, he is able to help it land safely (with a little support by Belldandy.)
The Hearts of MachinesEdit
The Machiners story arc is quite interesting as it represents a theme present throughout the Oh My Goddess series. Most motorbike-oriented chapters already showed this faith in the "Hearts of Machines", now Keiichi's apparent mastery of engineering mechanics is summed up by one of the Machiners as "That is why I like you... You are probably one of few members of mankind to truly understand the hearts of machines" (OMG, Chapter 174 (FT).) Fujishima's enthusiasm for cars and motorcycles certainly is one of the origins for this theme, another element might be the frequent association of spirits to entities of human or non-human origin in the Japanese anime/manga culture.
In the end, a little mystery remains, when Keiichi sees that the tools he received from the Machiners as a sign of gratitude had amazing effects on all machines he worked on. Keiichi asks Belldandy why the Machiners came to precisely them and why they needed repairs if they had these tools themselves. The answer is partly subject to interpretation.
Belldandy: "Also, even though they have tools, they do not use them."
Belldandy: "It was necessary that Keiichi-san be the one to do the repairs."
... [after Keiichi's work on Chihiro's motorbike had stunning results]
Keiichi: "It can influence the nature of a machine with just one bolt? If it were like that, wouldn't everything connected to it be... and also, I touched the machiners, as well..."
Belldandy: "That's right... Keiichi-san was chosen... Because Keiichi-san's hands are hands that are loved even by machines."
— OMG, Chapter 176 (FT)