Part of the author comments: "It's a foot massage. It's a foot massage."

Is that so?

Where is her skirt..?

ルーミアもおもわずスカートが捲りあがるくらい気持ちよさそうです。これは足ツボマッサージです。　　これは足ツボマッサージです。

It's mentioned in the artist's comments, if someone can give this a quick translation.

"It seems it felt so good that Rumia accidentally lifted her skirt. It's a foot massage. It's a foot massage."

CapableScoutMan said:
"It seems it felt so good that Rumia accidentally lifted her skirt. It's a foot massage. It's a foot massage."

Well if the artist said it I don't really have much reason to doubt him, do I?