Aya's History filled in from the translated drama CDs
It can be justified that Kritiker thoroughly trained Aya to do the job of information gathering. Perhaps his uncle helped him become connected to Kritiker in order to avenge his family. At least two years must have passed before Aya joined Weiß as 'Aya'. In those two years:
- trained at a flower arrangement school in Aoba (Sendai) where he met Kikyou (a Kritiker agent so alike to Ran), and Shion who becomes his trainer when it comes to sword fighting. The school was only a coverup for the Sendai branch of Kritiker.
- A mission to uncover a gruesome S&M ring goes awry, leaving most of the team he was working with dead. Most, meaning some faked their deaths, along with a few betrayals.
- He meets a girl named Taiyou at a rehab clinic after recovering from that failed mission. He is under the guise of a gardener there, sent by the Tsushima branch of Kritiker. The clinic director is under pressure by the yakuza to relocate the rehab center so they could use their land, or be forced out. He meets Saitou who seems to be a flakey, rogue assassin for hire, who helps him out in the end.
- He joins Crashers later, replacing an injured team member, and learns that one person in the group has a sister named Taiyou, the girl from the rehab center. She recognized his voice, as she is blind. Aya was a smart alecky jerk during Crashers, and seemed to have mellowed out.
After the Weiß timeline but before Gluhen, his past comes back to haunt him while the flower shop travels in a mobile home, as Kikyou is not really dead, but part of an assassin group calling themselves Weiß. They are imposters and are killing those not even on the list to be killed. The mysterious leader of the group is none other than Shion. Aya kills Kikyou, and is haunted in his dreams by him on a constant basis. Shion also appears there, taunting him about being just a murdered like himself. Aya, who believed in all Shion had taught him, could not stop seeing him as his mentor although everything he was taught from that man was basically a lie. Aya still cannot deny how similar both he and Kikyou are in terms of vengeance for their fallen families. Kikyou joined Kritiker for the exact same reasons Aya did.
Shion, with Azami, Ayame, and Rindou, continue their murders and try to take over Kritiker by kidnapping Birman and demanding Persia hand over Kritiker to them. Manx is fatally wounded after her mission to retrieve Birman fails, and her agents are killed. She urges Weiß to kill Birman before she leaks information. Although they decide to rescue Birman, she uses Aya's gun on herself.
In the end, Ayame and Azami, who were murdering women for fun, are killed by Ken and Youji, and Aya has one final battle with Shion one on one. They both seem equally matched, but Shion's experience wins out. However, Aya pulls a gun on him and shoots him, saying that he's just a murderer, so why should he fight fair, and that Shion is so obsessed with the sword that he doesn't think of other factors like guns. Shion commits harakiri, leaving the victory to Aya, or so it seems.
Another two years have passed, and Aya is in NY working with another assassination group there. Omi, now Persia, seems to have called him back. He returns to Japan to find the others and recruit new members. Youji is, basically, a whore and uses drugs. Ken is homeless, and Mamoru has taken up the Takatori name and made it into something positive. Kyou was a sort of hired muscle, using the money to go to high school, and it something to do with his little brother's death.