You can buy peeled amaebi (sweet shrimp), tobiko caviar and shiso flowers or leaves in any shop specialising in Japanese ingredients. Place a large pot of salted water over a high flame.
But with the garlic, oil and chilli flakes as the starting point ... For even more umami, I add Chinese dried shrimp roe and fresh tobiko (flying fish) roe. This makes far more of the topping ...