This reveal lacks of build up or more accurately, lacks of hope. Because of Shade's obstruction, Tanpopo barely killed any Phantom at all so she won't feel much guilty with this reveal. This moment should be best place after Tanpopo overcomes Shade's obstruction, successfully kills one or many Phantom, feels proud about herself, hopeful about the future and then this reveal hit her. It will deal the maximum damage. Bonus if the grandfather has more time to develop to make this situation hurt more