“This is not an imitation of Arjuna...! Beware the sky, I think it is going to get bad.”
Brahmastra Kundala: O' Brahma, Curse Me (梵天よ、我を呪え, Bonten yo, Ware wo Noroe?) is a Noble Phantasm obtained by Karna from the Brahman Parashurama. It is a projectile that is granted his fiery attribute, Mana Burst (Flames), which from one blow is likened to a nuclear weapon. It will appear as a bow under the Archer class, and it will manifest as a projectile under other classes. Under its original design in Fate/complete material IV, it is called Karna's hidden Noble Phantasm and trump card, having bestowed Brahmastra with the sweltering heat effect of his Mana Burst to increase its already wide effective range and power exceptionally.
The usage of the ability in Fate/Extra CCC causes him to imbue his spear with flames by rapidly spinning it, and he subsequently throws it high into the air. Random projectiles of flame rain down over a period of time, and it is only utilized after Vasavi Shakti is deployed and Kavacha and Kundala is destroyed.
 Fate/Apocrypha material - STATUS: Lancer of Red, p.036-037
 Fate/complete material IV: Extra material - Fate/Apocrypha - Karna, p.300-301