I tried Kusefuku Shoten's "Nori Butter"! An evolved version of "nori no tsukudani" that goes well not only with rice, but also with bread!
An evolved version of "nori no tsukudani" (seaweed food boiled down in soy sauce) that makes your white rice taste even better! I found "Nori Butter" by Kuze Fuku Shoten! It is delicious not only on rice, but also on bread.