Why did the victim of the Akihabara massacre write a letter to the defendant?

The Akihabara massacre was an incident of mass murder that took place on 8 June 2008 in the Akihabara shopping quarter of Chiyoda, Tokyo, Japan. The perpetrator, 25-year-old Tomohiro Katō, drove into a crowd with a rented truck, initially killing three people and injuring two; he then stabbed at least twelve people using a dagger, killing four other people and injuring eight.

One of the victims in this case, Hiroshi Yuasa, sent a letter to defendant Kato. What was their reason?

Broadcast date: 27 July 2010 TV Tokyo evening news program, NEWS FINE