Long-term foreign investors are jumping on a seemingly unstoppable Nikkei rally amid expectations that Japan's famously frugal companies will start coughing up more cash to shareholders, analysts say.

"Many long-term global investors have been neutral or underweight on Japan equities but are now catching up to lock in the relatively higher earnings growth visibility," BNP Paribas chief Japan equity strategist Shun Maruyama told CNBC. "With dividends and share buybacks also expected to rise, cash equities buying by foreign investors is expected to continue in a sustained way."