formable schluter trim, but tbh that goes under the step curved tiles, not the risers, also I would have tiled the riser first in soldiers max 25mm width, and adhered the formable trim to the top of the riser, then cut the radius to that.
tip: butt the soldiers together and where the grout joint is, leave the 3mm joint, to make it look as though the riser is bent and the risers are bonded with the step ;-)
ps: love your safety footwear