Prepare the chashu pork: Roll the pork belly tightly and tie with kitchen twine. In a pot, sear the pork on all sides until browned. Add soy sauce, mirin, sake, sugar, garlic, and ginger. Cover with water and simmer for 1.5 hours. Let it cool, then slice thinly.

Make the broth: In a pot, combine chicken or pork broth with soy sauce, mirin, and sake. Simmer for 30 minutes. Adjust seasoning with salt if needed.

Prepare soft-boiled eggs: Boil eggs for 6-7 minutes, then cool in ice water. Peel and marinate in a mix of soy sauce, mirin, and water for at least 30 minutes.

Cook the noodles: Boil ramen noodles according to package instructions (usually 1-2 minutes). Drain and rinse under cold water to stop cooking.

Assemble the ramen: In each bowl, place cooked noodles. Pour hot broth over the noodles. Arrange chashu slices, halved soft-boiled eggs, nori, bean sprouts, bamboo shoots, and green onions on top.

Finish with a drizzle of sesame oil and chili oil (if using). Serve immediately.