When choosing a character for abilities like "Choose one character with 5000 or less BP on your opponent's front line and sideline it" which include the instruction to "choose" a character, this ability forces the player to place one card from their hand into their sideline as an additional cost in order to choose this character. The player may instead not pay and choose a different character. Or, if the option is allowed, they may choose zero characters. If they have no cards in their hand, this character cannot be chosen.