How deep is the part of the pond that is in the shade? Are you wanting submerged plants or does it matter? If you can set potted pond plants on a variety of platforms of different heights you can use iris plants and others that grow in the shade keeping the top part of the pot out of the water so the koi can't dig.

The trouble is, koi eat plants and so many hardcore koi people will tell you...either have plants or have koi, but don't have both. I prefer that my koi are in a plant free pond and the plants are in a separate pond, they can be connected with plumbing since the plants make a nice natural organic filtering system.

Try Googling "shade pond plants" and find ones that will grow vertical and can have the top surface of the pot out of the water.

Good luck.

Dark Lotus