"Eight sword" is Kenpachi's name.
In that picture Kenpachi's saying that swinging with both hands is stronger than swinging with one.
Kenpachi: "...Man... no choice then... guess I'll give "kendo" a try for the first time in awhile."
"Don't you know? You swing your sword stronger with two hands than with one."
So he grips his sword with both hands and swings down.
Lol il va le déchirer sans technique de shikai
Trop fort ce Kenpachi