Slice the green onion thinly and soak in water for 5 minutes, then drain. Chop the cilantro into bite-sized pieces.

Boil water in a pot, cook the vermicelli according to package instructions, rinse with cold water, and drain.

In a pot, heat water and sake. Once boiling, add the chicken breast, cover, and simmer on low heat for 7–8 minutes until cooked through. Remove the chicken and skim off any foam. Add the remaining soup base ingredients and bring to a boil. Add the vermicelli and simmer for 30 seconds.

Slice the cooked chicken thinly.