TCG Rulings

• This effect will only activate if you attack your opponent directly and successfully inflict damage. If your opponent took 0 damage because of “Waboku,” this effect will not activate.^[1]

Judge Program Forum Rulings

• If Player A attacks directly with "X-Saber Airbellum" while Player B has "Gorz the Emissary of Darkness" in their hand, both effects can be activated during the Damage Step forming a Chain. "X-Saber Airbellum" will be Chain Link 1 (as mandatory effect), and "Gorz the Emissary of Darkness" will be Chain Link 2 (as optional effect). So first "Gorz the Emissary of Darkness" will be Special Summoned to the Field and then "X-Saber Airbellum" will discard 1 random card from Player B's hand.^[2]

References

1. ↑ Konami Gameplay FAQ: Starter Deck 2009 – Card Rulings (Version 1.0)
2. ↑ Konami Judge Program Forum: Damage Step: X-Saber Airbellum vs Gorz