翻译中文原文:さいがわら

赛の河原（さいのかわら）かな？

The phrase means "unrewarded job" or "endless efforts in vain".

赛の河原 is the shore of the river 三途の川, which devide this world and another world. Dead men go to 三途の川, 7 days after they died.
At 赛の河原 shore,dead children always tried, or they have to, make tower by heap up the pebbles on the shore, but every time they have almost finished, just before they complete building, the tower is always broken by 地狱の鬼. As a result, dead children should continue to build a tower endlessly. It is a kind of pain continue forever.

Well, this is a Japanese Buddism story of 赛の河原 well-known in Japan. Related to this story, Japanese people often say to "endless efforts" or "unrewarded jobs" as "赛の河原の石积み"(さいのかわらのいしつみ、endless building a tower at 赛の河原,the shore of 三途の川), "赛の河原で石を积む" or shorter, "赛の河原".

稻草

赛瓦

日文中没有这个词汇