The third one became operational on 9 June 2014, six year early due to post-power demand from the Great East Japan earthquake.

[4][5] The upper reservoir for the power station is created by the Kamihikawa Dam at 35°42′58″N 138°49′57″E / 35.71611°N 138.83250°E / 35.71611; 138.83250 (Kamihikawa Dam) which is a 87 metres (285 ft) tall and 494-metre (1,621 ft) long rock-fill embankment type.

[2] The lower reservoir is formed by the Kazunogawa Dam (葛野川ダム), which uses water from the Sagami River system.

[3] When energy demand is high, water from the upper reservoir is released down to the underground power station via a single 3.3 kilometres (2.1 mi) long headrace tunnel which splits into two 1.8 kilometres (1.1 mi) tunnels before each separate into two 620 metres (2,030 ft) long penstocks.

Each penstock feeds a single reversible 400 MW Francis turbine-generator with water before it is released into a 3.3 kilometres (2.1 mi) long tailrace tunnel which discharges into the lower reservoir.