Search gender: all male female セイイチ Japanese Boy Names Variations. 41 names found. gender: all male female Name: seichi Katakana: セイイチ 0 Kanji: 勢一 Meaning: 勢Momentum 一One. The first. Kanji for the number 1 (one). To be the most superior. To begin, to put things together. You can save your favorite names with prev123 NAZUKE PON > About Japanese Names > Search Japanese Names By Kanji > セイイチ Japanese Boy Names Variations.