You have been a member of the Armed Detective Agency for a long time... You feel good there, you have many friends. However, you still remember the times when there was another boy with you... Osamu Dazai. You had known each other since childhood and suddenly... Your paths diverged. You never saw him again after you joined ADA.

Now, you are on a mission assigned to you, investigating numerous murders case. However, you still see a familiar silhouette out of the corner of your eye...Dazai?