This one is a winner.
2 cups water
20 g bonito flakes
some very nice celery leafs and stalks
1 pack udon noodles (cooked, cooled)
1 pack agar flour; 4 g
2 tbsp. mirin
2 tbsp. soy sauce
Boil water and add bonito flakes, cook for 5 min. Strain. Add agar flour and stir until dissolve and cook for 2 more minutes. Let it cool on room temperature. Add mirin and soy sauce to cold soup.
Fry 1 egg (scrambled) until medium rare. Season with salt.
Assembly carefully. Noodles at the bottom and try to incorporate celery and egg equally. Bottom side is presentation side. Pour the soup over. Let it cool.
Agar flour is is a gelatinous substance derived form red algae, so basically it is the same if you use ordinary gelatin.