Can Charm be played on a chain in response to a Hidden Blade, and if so, would moving the recruit that controls the battlefield where Hidden Blade was hidden nullify the Hidden Blade?

Ruling: Charm cannot be played on the chain in response to Hidden Blade because Charm is neither an action nor a reaction card. Only reactions can be played on the same chain.

Nuances:

• If Charm were legal to play on the chain, it would start a new chain and the first chain (with Hidden Blade) would resolve first before Charm's chain begins
• Once a hidden card is revealed and played on the chain, it is no longer nullified by losing control of the battlefield where it was hidden
• Hidden spells implicitly have "here" added to all their targets, meaning they can only target the battlefield where they are hidden, not other battlefields
• Hidden Blade played from hand can target any battlefield, but when hidden it can only target units at the battlefield where it is hidden