Mimato is a Het ship between Mimi and Yamato (Matt) in the Digimon Adventure, Digimon Adventure 02, and Digimon Tri series.
There is little interaction between the two in the series. Mimi does get upset when Yamato leaves the groups during the Dark Masters arc.
Many fans ship them because of the whole "rebel and princess" thing. It is also a case of "Ship the Spares" by Taiora fan to get Yamato with someone else so Sora can be free to be paired with Taichi.