Drake probably fell asleep quite well so I'll respond.
Not quite sure why words like 'lawyer', 'sue', 'court summon', 'trouble' are being tossed around scaring people unnecessary. The point Fluffy (now nicknamed as Uruwi it seems), makes is valid but not that dramatic. Especially not for you.
Simply put: You need to request permission when you want to use and publish your game which contains materials made by others (sprites, images, sfx). If the author provided "usage conditions", read and follow these. Otherwise when in doubt: Ask the author by PM, Twitter, E-mail etc. If the author is Japanese, he might not be able to communicate in English. Keep this in mind.
If you don't get a response, then don't publish. Never assume 'no response' means 'there are no objections'. This is a false assumption in general.