As long as this card remains face-up on the field, any effect of increasing your opponent's Life Points is changed to inflict the same amount of points in damage to your opponent's Life Points.
Rulings
Individual Card FAQs
If you have this card and "Snatch Steal" on the field, the opponent will take 1000 points of damage during each of his/her Standby Phases and you still control their equipped monster.
If you have this card on the field and activate "Rain of Mercy" you gain 1000 Life Points and the opponent takes 1000 points of damage.
If the opponent activates "Dian Keto the Cure Master", you can chain this card and the opponent will take 1000 points of damage instead of gaining Life Points. If the opponent chains "Mystical Space Typhoon" to your "Bad Reaction to Simochi", they will gain the 1000 Life Points.
If the opponent activates "Nutrient Z" in the Damage Step, you cannot chain "Bad Reaction to Simochi" since it cannot be activated in the Damage Step. If "Bad Reaction to Simochi" was already active on the field, its effect would apply to "Nutrient Z".
Multiple copies of this card are not cumulative. If you have 2 copies of "Bad Reaction to Simochi" on the field and the opponent activates "Dian Keto the Cure Master", they only take 1000 points of damage.
Trap|
Continuous