Combine together in a saucepan the sake, mirin, soy, ginger and sugar, bring to a slow boil, turn down and simmer for 15 minutes. Strain and place into a small dish.
Skewer together the ocean trout pieces, asparagus spears and mushroom halves.
Brush four plates with a little of the yakitori glaze and set aside. Heat a heavy grill pan, lightly oil and sear the ocean trout skewers, brushing a little of the yakitori sauce over each side while they are cooking. Grill until just cooked, but still pink and glossy in the centre.
Present the skewers on the glaze accompanied with a side of rice, a radish, micro sorrel leaves and the sesame seeds.