Complex sentence: At first, he refused, but Ilahn eventually convinced him otherwise; on Elysia, Illahn used the power of the Sigil to drain and absorb the power of many of the First.
Split into simpler sentences: At first, of course, he refused, but Ilahn eventually managed to convince him otherwise. There, he used the power of the Sigil to drain and absorb the power of many of the First.