The diving whale—
how its tail keeps going
up!

Iyo-iyo here is a rendering of the Chinese po-po.
Huineng, the sixth Patriarch of Chinese zen used it in the 13th line of his Formless Gatha. Yung Hsi, one of his translators explaines it as “running hither and thither. It’s like waves that intermittently push those forward that are in front of them.”

Both Iyo-iyo and po-po have the Hybrid Sanskrit word ayavyaya as a source. Ayavyaya means coming-going.
The Lankavatara Sutra, one of 3 seminal zen-texts has in its 50th Chapter “I do not teach materialism, nor coming-and-going (ayavyaya)”. With these words the author critisizes the materialist Lokayata-trend of Indian philosophy.
The Sutra on the Unlimited Life of the Threefold Body (transl. Paul Swanson) also speaks of ayavyaya when it says that the Original Buddha neither comes nor goes.

Buson doesn’t come accross as a zen priest, but as a pupil of haiku masters who knew their zen sources and stock phrases he must have been aware of at least Huineng’s use of po po.

I really like your translation! Short and sweet.

About Buson’s death poem:
[Shira ume ni akuru yo bakari to nari ni keri]
The night almost past,
through the white plum blossoms
a glimpse of dawn.

A long time ago I wrote a short article for a Dutch haiku magazine on Bashô’s death poem, and also mentioned Buson’s there. I remember one or more on the commentaries on Buson’s death poem stressing that he not only died shortly before dawn, but also at the end of winter. So the plum blossoms are the perfect kigo for the onset of spring, but I think they also signify the start of a new phase, because Buson is dying. Sort of like a new spring in a new place: Amidha’s Western Paradise.

My Dutch rendering of the poem at the time translates something like:

As of today
the dawn shines
plum blossom white.

I liked that haiku too — in fact, my original title for the post was “Peony hellmouth: haiku of Yosa Buson.” You’re right, it is the kind of transition one would expect in an art film. And the poet may indeed have intended the kind of defanging conversion of harm into beauty you suggest. Harold Henderson’s commentary says that interpretors are divided about whether this is a religious poem, or simply one that uses religious imagery. I think Buson meant it to work either way.

‘The King of Hell’s mouth:
peony petals ready
to be spat out.’

I’ll carry this one with me today on my drive to a dental appointment in Machynlleth! Actually I find the words bewitching and oddly sexy. If I were a film-maker I’d get a lot of mileage out of that image. It also brings to mind a turn of phrase by a Buddhist friend who refers to those moments when a deed intended to harm you doesn’t work out as the perpetrator intended, and brings unexpected blessings instead. She refers to this as ‘Arrows into Flowers’.