if your budget is low, take in mind you need at minimum 5 egacha to ensure at least one SEC (either alpha or beta, R or SR). And chances are lower if you are starting with event gacha.

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FYI, i have almost 16 months in PPS, no alpha until now (pool stuck with 6 SR left).

You get R and SR from e-gacha, N from n-gacha. They cycle the images of the slayers on the event page.