"Lmao, why is Japan caring about the sanctity of a constitution forced onto them after losing WW2 after being teleported into a different world?"
Although I do agree that they need to revise many things considering that the era of this world may well be considered pre-WW1 (countries are mostly short sighted and are too reliant with their own military might), Japan needs to:
1. Revise the constitution where the nation may not support peaceful allied nation.
2. Allow, if not force, its citizens to be armed with lethal forces (firearms) in case of spies or potential other immediate unpredictable harm.
3. Increase military spending and begin military research as soon as possible (1% to anywhere from 5% to 10% for the first year).
4. Use the increased military spending to fund for military satellites and active army personnel.