Hello,

> For example: the Japanese <"> is used as symbol for [+voiced]

correct.

> and de <º>
> is used somewhat as symbol for [interrupted]

Not quite!
The han-dakuten is used for gemination of consonants, that is representation
of "long" consonants, which can either be unvoiced plosives (e.g. "hatten")
or, again unvoiced, fricatives (e.g. "zasshi").

Regards,
Berthold