Sear the beef chunks in a skillet until golden brown, then transfer to the slow cooker.
Sauté onions, ginger, and garlic in the skillet until fragrant; add to the slow cooker.
Combine beef broth, soy sauce, mirin alternative, rice vinegar, brown sugar, chili garlic sauce, star anise pods, and cinnamon stick in the slow cooker.
Cook on low for 7-8 hours or high for 4-5 hours until beef is tender.
Add bok choy and mushrooms; cook on high for an additional 15-20 minutes.
Thicken broth with a cornstarch slurry if desired.
Prepare ramen noodles separately; serve topped with broth, beef, soft-boiled eggs, scallions, and sesame seeds.