Ideco as a US citizen (PR in Japan)

A few years ago, the company I worked for (in Japan) had me enrolled in their pension plan, and I was making contributions. Retrospectively, I probably shouldn't have been as a US citizen in Japan- I have no idea if any of the funds they were invested in fall under PFIC or not, I may have been inadvertently breaking some rules there.

Since leaving that company, the funds in that program (about ￥750,000) have been transferred to Nihon Record Keeping Network and every 6 months or so I get an envelope of papers showing the amount and strongly recommending that I open an IDECO and transfer the money into that (My current company does not have any pension plan it could roll over into).

As a US citizen, IDECO is pretty much worthless or at the very least not worth the hassle, from what I've read, due to the possibility of investing in PFICs, complicating tax filing in the US (I still file in the US, but I don't make over the FEIE limits, so I don't need to pay).

I'm finally trying to sort this mess out. Leaving the money sitting with Nihon Record Keeping Network means zero investment income on it (I'm 54, so probably 10+ years to go at least), and there are some warnings about possibly not being able to withdraw it upon retirement if left where it is.

Under my circumstances, should I open an IDECO and leave the money there as cash? At least it would eventually be available. Transfer to an IDECO and be very careful about how it's invested to avoid PFICs, if that's even possible?