Answer:
a) 吉 -> 吐 -> 城 -> 盛
吉 KICHI, KITSU, yoshi - good luck
吐 TOU, ha(ku) - spew, vomit, give vent to
城 JOU, shiro - castle
盛 SEI, JOU, mo(ru), saka(n), saka(ru) - prosperous, energetic, serve food
b) 皆 -> 皇 -> 理 -> 黒
皆 KAI, mina - all
皇 KOU, OU - emperor
理 RI - reason, logic
黒 KOKU, kuro(i) - black