Just pulled out HOTD Volume 4 and 5.
Volume 4 ends with Act 17 The Sword And The Dead
Which tells of when Seako tells Takeshi she was a "monster" before They appeared. Which the anime places out of place. I can go into more about this if you would like, but it is spoilers to both the Anime and Manga. I would like to stay away from that.
Volume 5 starts with Act 18 Legend Of The Dead
Which is them meeting the people in the Mall, which the anime ends with them reaching it.
Edit: I will discuss a spoiler in it.
Volume 5 covers all their mall time and ends with them getting ready to leave, so no way is it in the anime. Volume 6 covers them leaving and deals with some side characters mainly that they meet at the mall.