Japan builds purpose-designed carriers without conversion rules

What would Japan build instead of converting Akagi and Kaga under Washington Treaty rules?

Japan would build carriers from scratch, probably adapting a battlecruiser or cruiser hull form to a purpose-designed carrier.

Removing the Washington Treaty does not remove aircraft carriers because naval aviation is already under development. The design path shifts away from treaty-driven conversions toward purpose-built ships. Battlecruiser or cruiser hull forms could provide the speed and internal volume required. Japan would therefore build a carrier around a large fast hull instead of converting Akagi or Kaga under Washington rules.