Just an advice:
If you really interested in studying in Japan, you should start learning Japanese Language as soon as possible (Form 2 maybe?). Early planning will benefit you in the end.

And straight away attend Language Schools right after SPM!! Yes you got it right! AFTER SPM!! Because in Japan, they will just look at how many years you have completed your studies in your home country, disregarding which qualifications you have, and your results in EJU comes on top of everything else. If not mistaken, only Language Schools provide preparation for EJU so just focus on getting good grades in EJU is enough to get into any Japan Universities!!!

Taking Pre-U Qualifications is not recommended because 90% of the case you will still have to study for EJU, which is a waste of your 2 years time to study Pre-U again. Got this information from Facon Education Fair 2015 at KLCC.