<p>The kanji used for active, 能動的, means that what you do influences/affects others, as opposed to 受動的 which is the antonym. When you read the entire description, it reads that the user gains the right to charge when their action is active (influencing/affecting others), which are attacks and not shields. Not once has Bell ever used Argonaut to shield himself from something, not to mention the skill is also described as a "hero's strike"
</p>