Much of the KHR fandom is ruled by numbers. These are abbreviations for characters, designated by the Japanese fans, based on the two Japanese number systems. Since they are codes used by the international fandom, it is best that you become familiar with the system, and the usual number codes.
27 = 2-7 = tsu/two-na (Sawada Tsuna)
80 = 8-0 = ya-ma (Yamamoto Takeshi)
Remember that KHR is filled with cute guys, and the fandom is filled with shonen-ai pairings. This is partly the reason why all the number codes were created. Knowing the codes will help you know what kind of fanart/fanfic you are getting.
Now some multiplication lessons.
5986 = 59 x 86 = go-ku(dera) x ha-ru
– Gokudera Hayato is paired with Miura Haru, in a non-shonen-ai but fandom-only pairing.
6996 = 69 x 96 = mu-ku(ro) or ro-ku(do) x ku-ro(mu)/Chrome
– Rokudo Mukuro is paired with Chrome Dokuro, another popular non-shonen-ai pairing.
8059 = 80 x 59 = ya-ma(moto) x go-ku(dera)
– This means that Yamamoto is seme and Gokudera is uke.
– This is one of the “canon” pairings, seeing that these two are always at each other and are almost always seen together.
6918 = 69 x 18 = ro-ku(do) x (h)i-ba(ri)
– Rokudo Mukuro is seme and Hibari Kyoya is uke.
– “Canon” pairing in the sense that these two are always itching to get together and have a good blood match. ^^;;
* These are NOT canon pairings, in the way Tsuna/Kyoko or even Bianchi/Reborn is a canon pair, officially part of the storyline. These are the most common of the fandom-accepted yaoi pairings, implied often enough in the main text without anyone having to stretch the imagination too much. (^^;) I made examples of these, since these are two 4-digit numbers you will see pretty often.
Number codes are given with each character profile.