* Nikkei in 6th day of decline, falls below 25-day avrg * Rally that began in early June looks to be over * BOJ's policy tweak, rate cuts elsewhere fail to impress * Asahi Glass falls after dismal earnings * Hi-tech, industrials also weak on global slowdown fear By Hideyuki Sano TOKYO, July 12 (Reuters) - Japan's Nikkei share average posted its biggest fall in more than a month, dropping below major support at its 25-day moving average on Thursday after the Bank of Japan only offered minor tweaks to its easing strategy. With monetary stimulus around the world overwhelmed by mounting signs of global slowdown, market players expect further downside as they fear companies will have to revise down their profit outlooks.