Hi Yukio, good to hear from you again.
Spaghetti is popular in Japan? I thought you only ate rice and noodles ;-)
Instead of soaking the spaghetti in cold water for a long time, you can boil for 1 minute then switch the stove off and leave the spaghetti in the hot water for 10-15 minutes. Wrap the pot in insulation to keep it hot.