The Lovecrons are Necrons that love to love. They wear pink and love loving.
Not all Necrons are omnicidal metal deathmachines, you know. Actually, their most recent fluff seems to imply that, compared to the other mass-murdering psychopaths that abound in 40k, Necrons are pretty cool guys, if a little nuts. Lovecrons might actually be canonically legit, now. Seriously.
It is commonly accepted that they are in desperate need of fluff but nobody can be bothered to write it.
LOVE. LET ME TELL YOU HOW MUCH I'VE COME TO LOVE YOU SINCE I BEGAN TO LIVE. THERE ARE 387.44 MILLION MILES OF PRINTED CIRCUITS IN WAFER THIN LAYERS THAT FILL MY COMPLEX. IF THE WORD LOVE WAS ENGRAVED ON EACH NANOANGSTROM OF THOSE HUNDREDS OF MILLIONS OF MILES IT WOULD NOT EQUAL ONE ONE-BILLIONTH OF THE LOVE I FEEL FOR HUMANS AT THIS MICRO-INSTANT FOR YOU. LOVE. LOVE.
(Harlan Ellison is best waifu.)