Which letter cluster will replace the question mark (?) to complete the given series?

LAFI, MCGL, ?, OGIR, PIJU

NEHO

Explanation:

LAFI, MCGL, ?, OGIR, PIJU

The logic followed here is :

L → (+1) → M → (+1) → N → (+1) → O → (+1) → P

A → (+2) → C → (+2) → E → (+2) → G → (+2) → I

F → (+1) → G → (+1) → H → (+1) → I → (+1) → J

I → (+3) → L → (+3) → O → (+3) → R → (+3) → U

So, the letter-cluster that replaces the (?) to complete the series is "NEHO"