The item Vajra is said to mean diamond/adamantine or thunderbolt in sanskrit. Its association with diamonds has it symbolize both purity and indestructibility. The Vajra is also used to symbolize enlightenment due to this association.
—Item description, Persona Q2: New Cinema Labyrinth
The Vajra is a weapon for Koromaru only. It can be purchased from the Workshop for ¥62,000 after selling Akashic Record, found in the Theater District, Black Tangle, dropped by Phunbaba, and Luxury Lashes, dropped by Tyranniqueen.
Halves HP cost / Ma +4 / Ag +4
(Akashic Record x1, Black Tangle x1, Luxury Lashes x1)
Persona 5 Strikers
"A replica of Buddhist equipment named after Indra's mystical weapon."