Cut the mentaiko open and extract the contents.

Remove the tendons from the chicken tenders. In a bowl, combine chicken, sake, and salt and pepper, and massage well.

Cover the bowl with plastic wrap and microwave at 600W for 4 minutes. Let it cool with the wrap on, then shred the chicken by hand.

Cut off the roots of the kaiware sprouts. In a bowl, mix shredded chicken, kaiware, mentaiko, and mayonnaise.

Boil water in a pot and cook the somen noodles according to package instructions. Rinse under cold water and drain well.