Fuyumi Irisu
Fuyumi is Chitanda's upperclassman. They are on good terms and seem to be good friends, although Irisu comments that Eru struggles in making others do her bidding.

Kaho Juumonji
Kaho is a close acquaintance of Eru's. Primarily, their familiarity stemmed from the social obligations between the Chitanda and Juumonji families. During New Year's Eve, the Chitanda family makes sure to bring presents to the Juumonji family.

I'm curious, I can't stop thinking about it!

"That's because you've never taken a close look at yourself."[14]
"His brain, I feel like i want to open it up and take a peek inside."[3]
"I find myself hard to understand sometimes"[15]
"I like to avoid getting tired"[15]
"I just... I have to know!"[16]
"If you can never get mad at anything, I'm pretty sure there's nothing you like either!"[15]

Eru's surname Chitanda means "thousand" (千) (chi), "anti" (反) (tan) and "field, rice paddy" (田) (ta/da).

Eru is good at cooking.
Eru is vulnerable to alcohol and caffeine.
Eru's favorite drink is Matcha milk.[1]
Eru stands at 160 cm (5'3") and weighs at 54 kg (119 lbs)
Surprisingly, by her first year's mid-term test, Eru is ranked sixth in her year that she is often called "top student".
Eru apparently has a good sense of hearing and smell, as she is able to hear and smell things that other characters are unable to.
Eru is also quite physically strong. Evidence showed in episode 11.5 where she can easily lift and carry Mayaka. Satoshi also commented about her strength in that very same scene.
Eru is very meticulous as she sees details other people might fail to see.

In Episode 20, Eru claims that she has excellent night vision.
Eru visual acuity is 2.0 which means her vision is twice as sharp as a normal person within the same distance of a target.[1]

Eru has not read a mystery novel for years, as claimed by herself.
Satomi Sato (Chitanda's seiyu) and Daisuke Sakaguchi (Satoshi Fukube's seiyu) sung "Update Go Issho ni" and "Itsuka Bokura no Epilogue" in Hyouka Net Radio "Kotenbu no Kuttaku" Theme song CD.
Houtarou specified her as The Fool of the tarot cards.
Besides Jun Sekitani, two more relatives of Eru were mentioned in the light novel series; Shounosuke Chitanda (grandfather) in volume 3 and Tetsugo Chitanda (father) in volume 4. However, only Tetsugo was mentioned in the anime series.