Shimano's LT-4 series of derailleurs were strange 4-speed devices that I believe were designed for children's bicycles (and possibly some women's bicycles) aimed at the Japanese domestic market.
The derailleurs are pressed steel offerings, clad in alluring plastic panels. They have an interestingly straight cable run and they integrate into full chain guards to keep those children clean and safe.
I have seen three different variants:
This example is a grey Shimano LT-4 (LT40).
This Shimano LT-4 (LT40) shares many parts and features with the Shimano LT-4 (LT45). So you may find it useful to look at the parts explosion for the Shimano LT-4 (LT45), and the service instructions for Shimano LT-4 (LT45).