I never saw or heard the word before, but after searching around the web I agree with your translation and your analysis.
If the words
are Mom and Sushi, I suppose E.S. wouldn't have given us the clue 'Okaasan' (mother) as someone's mother is also likely to be an aunt, niece, and/or babysitter? The Japanese for 'father' is a better clue to lead us to Sushi and Mom.
I think we should definitely follow the Japanese connection first so I'll do that now. Assuming we're right then we could wait and see what Kael thinks before we make our final guess.
Guess: Sushi