To train or rather, raise Ki, many things could be done. The summation of these actions was referred to as Ki Plundering.
'To absorb the vital energy of heaven and earth, making it your own...'
That was the description the system had given for the act of Ki Plundering.
Pushing the body, or performing strenuous activities like fighting and exercising could raise the latent amount of Ki one possessed. However, during a battle, one couldn't raise their latent amount of Ki. It was still possible to recover spent Ki though.
The most effective and efficient way to raise latent Ki was by exercising and making use of the passive Ki acquisition rate simultaneously. As the Tiers of his Ki Plundering technique increased, the rate at which he could increase his latent amount of Ki also increased.
However, it would require more and more effort to progress to the next Tier...
'Let's start then...'