Asian movie about a guy with a bad posture looking after two kids from a lady who has a disease to destroy the world or something

I remember watching this movie around 9-10 years ago but I don’t remember the title.

It’s about some asian dude who kinda looks like L Lawliet from Death Note and he has a bad posture and he’s super smart (I think) and he encounters these 2 children that he has to look after; But theres also this lady who has some virus or disease or something that she’s going to spread to people (She herself doesn’t have the disease but i remember her holding this yellow syringe with it?)

I vaguely remember 3 scenes from the movie:

One theres these 2 asian women possibly sent from the lady to kill the two children but the guy saves the children.

two: The guy is drawing on a chalk board and the children tell him he should fix his posture and sit up right in which he tries to.

three: The lady is onboard a plane in which she releases the virus to people but the virus also infects herself. The people look like they’re all in pain and have dots on their face screaming and crying on the plane.

I can’t really remember the movie title image but i think it’s the asian guy standing in the middle and behind him is just chaos or something??

Anyways I really hope to find this movie please help.