In a saucepan, combine water, hondashi, sugar, sake, mirin, and soy sauce. Simmer on medium heat and stir until sugar is dissolved.
Add minced ginger and onions and cook for 5 minutes so the onions soften up.
Add sliced beef and cook for a 5 minutes until the beef is no longer raw.
Serve on top of hot rice and garnish with an onsen tamago, green onion, pickled ginger, and togarashi.
