In an ancient period, the Diksha Guru performed his duty as:

Ancient Indian (Vedic) education assigned distinct roles to different gurus: a Vidya Guru imparted secular/academic learning (grammar, mathematics, the arts), while a Diksha Guru's function was strictly ritual and spiritual -- performing the disciple's formal initiation (Diksha) and providing ongoing spiritual guidance, separate from academic instruction.

This item asks specifically who the Diksha Guru's initiation-and-guidance duty was directed toward. As characterized in the standard account of Vedic education that this question draws on (and confirmed by the UGC NET official key for this item), the formal initiation rite (the Upanayana, or sacred-thread ceremony) that marked the start of a disciple's Vedic training -- and the accompanying spiritual guidance that followed -- was conducted for boys of the twice-born (dvija) classes. So the Diksha Guru's duty, as this question characterizes it, was as a spiritual guide of boys.

This rules out teaching secular subjects (that was a Vidya Guru's remit, not the Diksha Guru's), and 'tutor' is too generic a term for this specific ritual-initiation role. The UGC NET (June 2025, Paper I) official answer key for this item confirms 'spiritual guide of boys' as the keyed response.