「ひ、ひみつだ！ひみつ！」

矢印の場所は洗ってる場所。なので、察してください。
あまり追及すると涙目で恥ずかしがってしまいます。

お風呂に入るときの妖夢ちゃん＞ post #1682268

"I-It's a secret! A secret!"

The place the arrow is pointing is where she washes. Please take a guess at it.
After briefly asking about it she became teary-eyed and blushed thoroughly.

Youmu-chan when taking a bath > post #1682268