[Boatanchors] Japanese schematic diagram symbol

[Henry Meils]

Might just be a symbol that shows a capacitor using a (specific kind of ?) dialectric material. Did you check other Japanese diagrams where the same symbol is used in an obvious function? (How do they represent quartz xtals?)
Usually a diagram component can be reasoned out by its probable function -  apparantly your diagram is not so obvious.
Why not find a bi-lingual Japanese (ham)radio/electonics website and ask them?
Have fun.
73  Henry, OZ1UF, Cph. DK