One of premier and most prolific mangaka dealing with futanari and the related themes of gender warping is ひねもすのたり / Hinemosunotari (also rendered as 終日庵), and he probably comes at or near the top of this particular sexual niche. Whether the genre appeals or not, it is not difficult to see why he has attained such popularity with his works, uniformly of a high standard and tightly focused on the prospect of hermaphroditic adventures as they are.
As he keenly admits, the proportion of futanari themed works he outputs is extremely high; there are additionally a variety of allied themes of crossdressing and the like featuring strongly. Lesbianism also features commonly. He has penned some fairly normal works, though they are definitely in the minority.
His latest compilation “READ ME!”, is very good, probably his best so far, though I would not say there is great deal of difference between his works. The story selected here probably serves as a good exemplar of his works, as well as being a favourite.
His major works are his compilations, all of which are similarly good. He also publishes dojinshi prolifically, though these aren’t really distinguished from his main works, containing a high proportion of original work. Getting hold of any of these works is unlikely to be difficult, whether in print or otherwise.
If I were to level any criticism at him (and I can’t say I’m particularly inclined to do so), it would be that his works lack variety – I’m not suggesting he move away from his favoured themes of gender bending (heaven forfend), but a greater variety within that genre would be welcome – looking through his works I get the impression that at times he is repeating himself.
It might also be said of him that his illustrative style hasn’t really developed very much from his earlier works – since I don’t think it is yet perfect (though nobody could say it is not highly accomplished), some more development would be heartening to see, particularly over a seven year span. Perhaps this is just a question of individual taste.
At any rate, Hinemosunotari is one of the, if not the, premier mangaka dealing with futanari and similar, so should this genre appeal in the slightest, it is easy to recommend him.