Hi ludo974
It's background image set for section which has this class suffix: .row-feature.row-feature-bg
.row-feature.row-feature-bg {
background: url("../images/custom-bg.png") no-repeat bottom right;
}
the image locates in: /templates/ja_sugite/images/custom-bg.png
You can replace with your own image.
In case you want to remove it, you can override by this custom css:
.row-feature.row-feature-bg {
background: none !important;
}