TLDR: Bochet the Buckwheat!!!
Buckwheat is my favorite variety of honey on things like toast, so when I first got into mead making, it was at the top of my to-do list. Others suggested using only a hint of buckwheat with the majority of the honey coming from clover or orange blossom to cover up the horrible flavor. My reaction was that if the flavor is horrible then why include it in the first place, and if the flavor is as amazing as buckwheat honey is on toast, then don't dilute it. Some sources said if you back sweeten it enough with a neutral honey it becomes good, but I like my mead dry – if I wanted it to be sweet I would just eat the honey. Also, I am pretty sure urine would be delicious if it were back sweetened enough (although I have not tried it). Others said they thought it would be better after aging and promised to post an update, but never did. Another source said it as having a "barnyard" taste, just like the honey. I don't think the honey has that taste, so I proceeded with hope.
The outcome tasted like someone took fresh-cut lawnmower clippings, brewed tea with it, and added alcohol. I tried a couple variations with the same results. I tried letting it age for 2 years. That took some of the edge off, but it was never something I was going to serve guests.
My last ditch effort was to try a recipe from Man Made Mead:
. The key step being to bochet the honey, then just for fun add rum barrel oak chips. Since bocheting is such an intensive process I wanted to get all the experimentation out of it that I could. I divided the batch into 4 portions and made each with a different yeast. Premier Rouge, Premier Blanc, Q23, and Kveik. All four were amazing! They needed a bit of age to reach their full potential, like any other, but they were delicious without any back sweetening. It was everything I was wanting a buckwheat mead to be when I started. I’m posting this on every forum I find, since it took me a good 3 years to get from goal to success. May this help you in your brewing journey!