In a saucepan, combine soy sauce, water, rice vinegar, sugar, garlic, and ginger. Bring to a simmer over medium heat, stirring until sugar dissolves. Remove from heat and let cool.
Place eggs in a pot and cover with cold water. Bring to a boil, then lower heat to a simmer and cook for 7 minutes for a jammy yolk. Immediately transfer eggs to an ice bath to cool.
Once cooled, peel eggs and place them in the soy sauce mixture. Ensure eggs are fully submerged, cover, and marinate in the refrigerator for at least 4 hours, or up to 12 hours for deeper flavor.