Ajikan is a common esoteric practice, going back to Vajrayana in India and probably further. I suggest you read Richard Payne's "Ajikan; Ritual and Meditation in the Shingon Tradition." found in "Revisioning Kamakura Buddhism" it's pretty old 1998 but a good place to start. You might find the later "Tantric Buddhism in East Asia" 2005 ed. Richard K Payne helpful in understanding tantra and its place in Buddhism.
If I remember correctly Rev. Eijo said with a tone of disapproval Shingon shu were teaching Ajikan to laypeople, but who knows that was years ago over at e-sangha. Things may have changed.
ah here I found a link to Komyo-in the Shingon Shingi temple in france & ajikanttp://komyoin.free.fr/komyo-site/franca ... iques/kan/