Toshins are generally large Japanese investment trusts which invest in overseas assets. They are very popular in Japan because of the traditionally low interest rates available there and these trusts can earn 4.5% in Australia in the money market alone. Japanese investors put their money in these funds, in this case over 1 trillion Yen, and the trust then buys overseas assets. If they are buying say 3 billion AUD worth of Australian assets, then this will have a significant impact on the AUD/JPY market.
Some care is needed though when trading this information, as often time the issuer of the trust will have covered some percentage of the total in advance, so part of this information is already in the market. If the fund isn’t well subscribed, then the effect on AUD/JPY could even be negative.