Kazuha Hitachiin is Hikaru and Kaoru's grandmother on their mother's side. She's in her 50's. She is a talented artist in Ikebana (flower arrangement) and her Ikebana company is in its seventh generation.
Kazuha owns and motorbike and likes doing adventurous things. She is known to go travelling without warning, and even her family can only keep up with her whereabouts by word-of-mouth or spotting her in magazines. In contrast to her outgoing nature, her husband is meek and quiet, but accompanies her on all of her travels.
Kazuha loves to tease Hikaru and Kaoru but secretly holds them very dear, and it is seen that she actually carries one of the drawings that she insulted when they were only five. Her unusual hairstyle was created by the twins when they were very young during an attempt to pull a prank on her; ergo, anyone who insults her hair is immediately on her bad side (like Tamaki).
The other hosts meet her when she helps them dress for a club event, but shes leaves as quickly as she arrives. Haruhi never meets the woman, but by the twins's anecdotes, she thinks Kazuha's personality is exactly like theirs, though they deny it and claim that she's a terrible adult.