Cook the sushi rice with the dashi powder (or kelp) according to your rice cooker or pot instructions.
While rice cooks, heat the rice vinegar, sugar, and salt in a small pot over medium heat until sugar dissolves. Set aside β this is your sushi vinegar.
Cut nori into spooky shapes (eyes, mouths, cat ears) using small scissors or a craft knife. For the cat face, use a 6.5 cm round cookie cutter to cut two nori circles.
Fry the egg flat, let cool, then cut out two rounds with the same 6.5 cm cutter. Slice cucumber and radish into thin rounds.
When rice is done, pour the sushi vinegar over it and mix gently to season. Let cool slightly.
Place a piece of cling wrap on your work surface. Put your favorite topping (e.g., smoked salmon slice, egg round, cucumber slice) in the center of the wrap.
Scoop about 1/3 cup of seasoned rice on top of the topping. Gather the corners of the cling wrap and twist to form a tight ball. Gently shape with your hands.
Repeat with remaining toppings to make 16 sushi balls. Unwrap each ball and arrange on a serving plate.
Use chopsticks or tweezers to attach the nori decorations (jack-o-lantern face, cat whiskers). Pipe mayonnaise for details (like a catβs face).
Top the radish and cucumber sushi balls with a tiny bit of fish roe. Serve with soy sauce, mayo, and wasabi (optional).