User blog comment:Fallenbladr/Aizens Escape/@comment-5398287-20140817203128

Erm...Tosen exploded because of the unstable nature of his Hollowfied soul. Remember, Urahara explained in this final arc that the Visored would have basically blown up had he not accidentally stabilized their souls with the Hogyoku while looking for a cure to their condition. Tosen simply became a Shinigami/Hollow hybrid without any apparent stabilization, so he asploded. I'm pretty sure Aizen just smiled because he's Aizen, the biggest troll in the history of the series.