Friday was a big day for the world's largest pension fund, which posted its worst annual loss since the financial crisis and disclosed individual equity holdings for the first time. The two may be connected.

The list of domestic shares owned by the ¥134 trillion Government Pension Investment Fund hews closely to the benchmark Topix index, which isn't that surprising for a fund where almost 80 percent of investments are passive. But it means that in market downturns like in the past year, GPIF will struggle to increase assets.

The fund recorded a ¥5.3 trillion loss for the 12 months ended March, the largest decline in seven years. Japan stock holdings tumbled 10.8 percent. For Sumitomo Mitsui Asset Management Co., GPIF should branch out from hugging indexes.