If he's found guilty then he'll definitely get a prison sentence. No idea how long. What do they Japanese normally dish out for fraud and insider trading? Will they be able to prove he was involved in the shady business, though? Maybe they already have enough evidence or maybe not.
I heard at Euronews now that he was founded guilty for manipulation of data. According to the reporter he was access to the data of the customers and has manipulated those in order to have profits for himself. Otherwise it will not be arrested.