This is a clear issue in which. Theologically it can be argued that despite the names, angels and devils do not have genders, per say, merely feminine or masculine tendencies. However that does not help with referrals to them without using their names, presenting a lovely problem on fan pages, publications, and fan fiction, all forms in which a fan might find him or herself. 

In many other languages, this is dealt with by using a simple "sexless" address, however, English has none of these to boast of. Thus, when WISH was translated by Tokyopop, the idea to address Kohaku as either a "he" or "she" came up quite frequently, as did the issue of addressing Hisui. 

This of course, is, too, a problem related to pairings and relationships in WISH itself. Although Japanese society seems to have accepted shonen- or shoujo- ai (same-sex pairings) as a given when dealing with any time of story line, North America has not yet been completely accustomed to this. Most anime fans are accepting of the pairing no matter who is involved, but some protest at the so-called blatancy of such pairings.

Take Kohaku and Shuichiro for example: At first glance, Kohaku appears to be a girl, and stereotypically, acts far more feminine than her counterpart spiritually, Koyruu--who exudes mascunlinity. As Shuichiro also appears very masculine, it is little wonder why Tokyopop has decided to label Kohaku as a girl: people may not be able to picture Shuichiro with another man.

Hisui is also an ideal example. The angel master takes on a very maternal role, and Hisui's companion (husband, perhaps), Kokuyo, is more masculine then anyone else in the series. Thus, Hisui too, is often referred to as "she." However, it one looks closely at the drawings in the manga, one finds both Hisui and Kohaku flat-chested: though this may have been glanced over given the flowing lines of the clothing.

No matter what the case, WISH will remain as endearing as ever, despite the great gender debate. Though this site may refer to all parties as "he", it is not forcing its beliefs on you.

So remember, despite what they are called:

Angels and Angels

and 

Demons are Demons

~ angelic