Hagashi toro is very rare because it is so difficult to prepare and very labor intensive. The cut of maguro typically used for this preparation is located at the top of the tail or at the bottom of the belly. The chef painstakingly removes all pieces of tendon and sinew (talk about arduous knife work!), resulting in a completely soft texture that is simply spectacular.
Pictured above is a piece of hagashi toro, aged 13 days, from Sushi Yoshizumi in San Mateo, CA.