Pros
Have a good chance to be engaged in great projects (depending on the team you are assigned); Paid (compared with most other Japanese offices that does not pay their interns at all); Interns have their own working area, so there is less pressure than working side by side with your mentor, and it's easy to make friends; Good experience on your CV;
Cons
Long working hours, but you can get days off after deadlines. You might be asked to jump between 3 projects in a day. Not all staff speak English that well (which is understandable) so there might be confusions when working with some teams. Hard, very very hard to approach Japanese staffs unless on their team, but international staff are all very friendly.