Peel the garlic, slice the ginger with the skin on into approximately 5mm thick slices, and cut only the green part of the green onions
Pork thigh meat can be tied with cooking twine, but it's also okay not to tie it. The advantage of tying is that it helps it stay round.
Put water, sake, mirin, soy sauce, sugar, garlic, ginger, and green onions in a pot, bring to a boil, then turn off the heat.
Place the pork thigh meat in a frying pan over high heat and sear all sides until browned. Only sear the surface without cooking the inside.
Put the seared meat into the pot.
Place a makeshift lid made of aluminum foil on the pot.
Simmer over low heat for about 1 hour and 30 minutes.
Slice the cooked meat to complete the dish.