A carrier is never a defensive weapon. It is always an offensive weapon. Hence Japanese aren't allowed to operate them (the Izumo is classified as a multipurpose destroyer to circumvent this).
Japan has plenty of defensive weapons – 300+ modern fighters (F-2/F-15/F-35), ton of SAMs, 100 odd maritime patrol aircraft, extensive sensor capability including large numbers AWACS/AEW&C, dozens of warships and 22 submarines.
The carrier's role is unclear for the time being.
It lacks the aircraft numbers to operate over Japanese controlled uninhabited islands near China where Chinese could swarm long range Su-27/-30/J-11/J-16s and J-20 stealth fighters.
The ship and its escorts would also be very close to Chinese land based and ship based long range antishipping missiles (F-35B is too shortlegged).
It also lacks certain key capabilities – airborne AEW&C, aerial refuelling, aerial reconnaissance (F-35s aren't kitted out for this and lack range).
These kind of pocket carriers seem best for expeditionary warfare against low tech opponents.
checks out some 10/15mm railroad tracks for wargaming.
