Ryou's Parents are Foreign Spies.

After Episode 11a/ Chapter 13, what we know about Ryou's parent's "work" that puts the girl to Parental Abandonment are as follows:

They are posted outside of Japan.
They are extremely vital positions, although Kirin's mom and Ryou herself differ on how important they are; at least they make or break a city.
It's top-secret. Nobody is comfortable describing it, even when asked by a person as close as Kirin.
No family breaks allowed. Ryou still remember how her mother looks, but they haven't been seeing her for a whole year in in-universe time.
They think Ryou is enough of a Living MacGuffin to need a bodyguard. They even think Kirin needs a bodyguard.

It's hard to think of any other positions that fits these descriptions.

Chapter 28 gives one more hint: Ryou's mom's workplace can have "serious explosions."

Ryou's grandmother was taken out as a soft target.

She knew that she didn't have much time left so she passed the apron onto Akira.

She's just really good at keeping poses static when the camera is pointed in that direction during the final episode.