Bro dont ever thnk of removing it... it will ruin ur car.... the sound will be of bedford truck plus smell of exhaust gases will be terrible...
1. get engine tunning + throttle body service
2. CVT changed
3. mix 10-20% Hi-octane in full tank
4. use good engine oil....
Milage will be min 15km/l upto 19km/l
Dont mess up ur car by removing catalytic converter.... its there for a purpose...
if not satisfied go to Vitz owner/fan club and read... u may post again and u'll get the same answer... Best of lUck