User blog comment:B214/Question and Answers 6/@comment-26293136-20161029205102/@comment-29963364-20161030011914

There are three ways for a Sacred Gear wielder to get stronger.


 * Train to evolve their Sacred Gear without making themselves stronger.


 * Train to increase their own base stats without evolving their Sacred Gear.


 * Train themselves and their Sacred Gear simultaniously.

Issei is a prime example of the first case. His base stats (strength, endurance, speed, etc.) are very low, so instead of training to increase them, he works on mastering his Boosted Gear in order to compensate. However, as he trains, his stamina and endurance increase to immense levels. Which is good because the Boosted Gear requires it's wielder to possess a lot of that in order to use it's power properly.

Tobio Ikuse is a prime example of the third case. Rather than a "power boosting" Sacred Gear like Issei's Boosted Gear, Tobio's [Canis Lycaon] is more of a "supplimenting" Sacred Gear. Tobio can improve his Sacred Gear as much as he wants, but if his own stats don't increas as well, that's not going to matter. So he trained himself and his Sacred Gear simultaniously, which resulted in him achieving his "Abyss Side" Balance Breaker: ​​Perfectus Tenebrae Lykaon et Fortis Densus Laelaps.​