Answer:
a) 哲 -> 吐 -> 城 -> 盛
哲 TETSU - wisdom
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) 磨 -> 硝 -> 削 -> 帰
磨 MI, miga(ku) - polish, brush
硝 SHOU - saltpeter
削 SAKU, kezu(ru) - whittle down, delete, curtail
帰 KI, kae(ru), kae(su) - return