I'm just a bit of information from the official Inuyasha Trading Card Game website. Since none of this information is part of the rule book that comes with the game, I thought I just post it here to make it easy to find.
The three Keywords that appear on character cards are Aggressive, Defensive, and Regeneration.
Aggressive: When a character has this Keyword you may only activate it when this character attacks by discarding a card from your hand. Then you add the cost of that card to the attacking color of that character for the attack.
Defensive: When a character has this Keyword you may only activate it when this character is attacked by discarding a card from your hand. Then you add the cost of that card to the attacked color of that character for the attack.
Regeneration: When a character has this Keyword you may only activate it during the recovery phase. It that character is defeated you may discard a card from your hand to save them. This is the only Keyword that works when a character is defeated.
The three Keywords that appear on events are Modifier, Draw, and Shuffle.
Modifier: When an event has this Keyword and is in your hand. You may remove it from the game when a character you control is attacked or attacking to add the events deck cost to that attacked / attacking color.
Draw: When an event has this Keyword and is in your hand. As an action in battle you may remove it from the game to draw cards equal to the events deck cost.
Shuffle: When an event has this Keyword and is in your hand. As an action in battle you may remove it from the game to shuffle a number of cards from your discard pile equal to the events deck cost.