The "Yoko" that travels with Alucard in Aria of Sorrow is actually Succubus from SoTN.
Why else would "Yoko" have a Succubus-like HP absorbing effect? The other succubi "pretending" to be "Yoko" are thus mocking Succubus for this and not actually trying to fool anyone. (Or, if Alucard has trouble telling generations of people apart, it's possible he thinks he sees Sypha.)
