Necessary
The way the 'Fountain Bow and Arrow Cut' functioned was simple. When one used the first form, a curving slash will be drawn in the air, briefly creating the image of a bow as it beheads the enemy.
Moreover, if the foe succeeds in defending against the attack, while the bow arc is still in the air, one can employ the second form 'Fountain Arrow Cut' in order to unleash a straight strike just like an arrow that's been released from the string of a bow.
When the two are released together, they complement one another as an attack much more powerful than anticipated renders the opponent helpless by catching him off-guard.
Perceiving the incoming attack, Ra's countenance went wan in terror as he realized that since he had just unleashed his offense technique, he could not execute another one as there was no time for it!
'Am I going to die?' As he helplessly watched the upcoming sharp blade, all hope was about to leave him when an idea hit him.