Creating options is the least important step in changing an entrenched cultural norm. What you actually need is a measure to eliminate the symbolic repercussions of using those options.

In the early 2010s, Bay Area startups were famous for "unlimited vacation" policies that resulted in less overall time off because everyone was well aware that taking even a standard amount of vacation would signal a lack of devotion.

What's the solution? Mandatory benefits: make everyone use their allotment, even if they don't want to. Many large banks force all staff to take holidays not only to combat a culture of overwork, but also to prevent fraud by making sure everyone has a block of time where they have to hand over their work to someone else.

If the Japanese government were truly serious about the "ikumen" ideal, it would pass a law requiring 6 weeks of paternity leave. Of course, I doubt that's politically or culturally feasible.