In Jain Dharma, “Athai” means an eight‑day tapa (fast/vrat). People do it in different ways—like 8 continuous upavās, or 8 days of ayambil/ekaṣan—always with right faith, right knowledge, and right conduct.

Punya (spiritual merit) from Athai when done with pure bhāva:

• Strong nirjarā: shedding of accumulated karmas, especially those strengthened by anger, pride, deceit, and greed.
• Control of senses and mind: inner peace, steadiness in samyaktva (right faith).
• Tapa‑anushthān punya: supports progress on the path toward keval‑jñān and moksha.
• Auspicious fruits for future births: better inner capacities, good environments, and opportunities for dharma sādhanā. (These are secondary; the main fruit is purification.)

How to do for true punya:

• Maintain ahiṃsā, truthfulness, and humility; avoid show or pride.
• Keep pratikramaṇ, svādhyāy (scripture study), japa, and dhyān each day.
• Take only boiled water at prescribed times; observe gupti (control of body, speech, mind).
• Conclude properly with pachchakkhāṇ (pratyākhyān) and daan/forgiveness.

Traditions:

• Śvetāmbara and Digambara both honor Athai as tapa. Practical rules (water timings, daylight limits, etc.) may differ by tradition and local maryādā. Follow your guru’s guidance.

Remember: without right intention and non‑attachment, the outer fast gives little merit. With pure intention, even simple austerity brings great punya and karmic shedding.