Maruishi is solid. Their stuff is comparable to Centurion/Lotus/Panasonic and other Japanese built bikes (like the Schwinn and Bridgestones of Japan). Usually come with solid tubing (Ishiwata or Tange or something similar) and have good build quality. The Maruishi RX-7 was a solid racer comparable to the Centurion Expert series.
the tubing is Tange 900 cr-mo double butted , i found 2 bikes at my local bike shop. i had asked the owner if he had any vintage bike parts for sale so he took me in the back and we found two old boxes covered in dust with complete bike frames minus the wheelset . he said that they must have been there before 1990 from the labels so he gave me a great parts price .
Maruishi is Japan's oldest bicycle company. They started in 1884 by importing bicycles into Japan and during the 1970s they entered the USA market, setting up a subsidary to design and import bicycles. They appear to have hit their peak in the early 1980s. As previously stated, they were comparable to other major, Japanese brands. In other words, they were good value bicycles.
Based on the serial number, your bicycle is a 1988 model and curiously appears to have been built by Yokota, who at that time was the 2nd largest bicycle manufacturing in Japan. Tange 900 is an economical, seamed version of Tange #2. The rear derailleur appears to be Shimano Light Action which, in conjuction with the Tange 900 tubeset, would suggest a model with a retail price in the region of $300-$350 US.