There is a scene early in “Cutie and the Boxer” of 80-year-old Ushio Shinohara brushing his teeth — although attacking his teeth might be a better description. It’s a small detail, but like many in Zachary Heinzerling’s remarkable documentary debut, a carefully chosen one. The director wants us to understand Shinohara is a fierce man. The avant-garde artist is known for his “action” painting — boxing gloves are indeed involved. But as riveting as Shinohara is, the real artist the film is interested in is Noriko, Shinohara’s wife of 40 years. Unlike her frenetic husband, Noriko, 59, is the rock in the relationship, the lion tamer. The lion keeper. And an artistic voice in her own right. She had only recently picked up the brush again when filming began. Inky watercolors and soft brush strokes leaven her graphic comic book style. Her panels tell the story of a pig-tailed Cutie’s struggle with the Boxer. The film is an extraordinary testament to love, marriage and the artistic process — hard to know which is the most difficult. At Landmark’s Nuart Theatre for another week, it is already generating Oscar buzz. Not one to miss regardless.