The "You can Tribute this card from your hand or face-up from your side of the field; Tribute monsters from your hand or field, then Ritual Summon 1 "Nekroz" Ritual Monster from your hand whose Level exactly equals the total Levels of those monsters." effect is an Ignition Effect that is activated from the hand or field. (It does not target. Tributing this card is a cost to activate this effect. Tributing monsters and Ritual Summoning are not considered to happen simultaneously.)
A "Nekroz" Ritual Monster Summoned using this effect is treated as being properly Ritual Summoned.