Creating Shoyu Tamago is a straightforward process. Follow these step-by-step instructions to make your very own soy-marinated ramen eggs:

1. Prepare the Eggs: Bring a pot of water to a rolling boil. Carefully add the eggs and boil for 6-7 minutes for a soft, custard-like yolk.
2. Ice Bath: While the eggs are boiling, prepare a bowl filled with ice water. Once the timer goes off, transfer the eggs immediately to the ice bath for about 5-10 minutes to stop the cooking process.
3. Peel the Eggs: Gently crack the shells and peel the eggs under running water to make this easier. Set aside.
4. Make the Marinade: In a bowl, combine the soy sauce, mirin, water, sugar, and sesame oil (if using). Stir until the sugar is dissolved.
5. Marinate the Eggs: Place the peeled eggs in a zip-top bag or a shallow dish, pour the marinade over the eggs, ensuring they are fully submerged. If using a bag, remove as much air as possible before sealing.
6. Chill: Refrigerate the eggs for at least 4 hours, up to overnight, for maximum flavor infusion.
7. Remove and Slice: Once marinated, gently remove the eggs from the marinade. Slice in half to reveal that gorgeous yolk.
8. Garnish: Sprinkle with green onions and shichimi togarashi (if desired) for added flavor and presentation.

Following these simple steps will yield perfect Shoyu Tamago each time, elevating your ramen to restaurant-quality levels.