Answer:
鷲 SHUU, washi - eagle
鷹 taka - hawk
戦 SEN, tataka(u), ikusa - war, battle, fight
海 KAI, umi - sea
牛 GYUU, ushi - cow
And the winner is 西! They all represent teams in the Baseball Pacific League!
西 SAE, SEI, nishi - west - Seibu Lions
鷲 SHUU, washi - eagle - Rakuten Eagles
鷹 taka - hawk - Softbank Hawks
戦 SEN, tataka(u), ikusa - war, battle, fight - Nippon Ham Fighters
海 KAI, umi - sea - Lotte Marines
牛 GYUU, ushi - cow - Kintetsu Buffaloes