Kazuha Tooyama

Heiji Hattori and Kazuha Toyama grew up together and are easily each other's best friend and mutual love interest. They have gone at the same school since they were in pre-school. Neither of them have been shown to have other close friendships outside of their relationships with Shinichi and Ran, though Heiji does have a rivalry with fellow kendo practitioner Okita. They often spend time together, and Kazuha typically comes along when Heiji visits the Mouri's or vice versa, and is usually getting caught up with Heiji in criminal investigations. Kazuha and Heiji both wear twin good-luck charms that Kazuha made with pieces of the handcuff chain that stuck them together temporarily as children. Kazuha and Heiji have both shown jealousy when the other appears interested in someone else, even though they're not officially in a romantic relationship. Although, all their Jr. High School and High School classmates have commented that they're a couple. Their parents have known each other before they were even born. Making their families close.

At one time in their youth, Heiji had had the unfortunate idea of locking themselves together with a set of old handcuffs which had no key and could not be unlocked; as a result they had to involuntarily spend time together even on some rather intimate occasions (i.e., bathroom visits before the cuffs could be removed. As a reminder of this 'closeness' and for good luck, Kazuha fashioned two identical lucky charms, each incorporating a chain link from the cuffs, which she and Heiji have been wearing ever since. At some later point, Kazuha added a picture of Heiji into her own charm pouch.

Kazuha has a hot temper and can be highly critical of people around her. She has been hinted to have a high level of intelligence, as she was able to deduce a dying message in an episode even more quickly than either Ran or Kogoro could (albeit with slight help from Heiji). Moreover, she is highly confrontational, and unafraid of letting others know about her dislike, even showing no hesitation or concern in confronting Heiji in a men's restroom. This trait leads to frequent shouting matches with Heiji, but it also allowed her and Ran to forge a strong friendship despite the fact that Kazuha, believing that Ran was Heiji's new girlfriend, took an initial deep dislike to Ran out of jealousy. Affection and approval are apparently much harder for her to express, most significantly with regard to Heiji; she is perfectly aware of her feelings for him and, after a few initial attempts to deny it to Ran, openly discusses her love for Heiji with her. However, even when a good opening appears to discuss her feelings with him, she instead panics and does her best to pretend that she and Heiji are 'only friends'. Although she has tried and failed to confess to Heiji twice already, Kazuha is determined to make her feelings clear to him one day.

She also has a marked belief in spirits, good-luck charms, and other superstitions. Right from her first experience, she displayed her belief in the importance of hers and Heiji's omamori, charms which Kazuha made to protect her and Heiji from harm. And indeed, during the case in which this is revealed, Heiji lent Conan his omamori, and the metal inside the charm stopped a knife blade that could have killed Conan. On subsequent cases, Kazuha is quick to attribute mysterious shadows and strange events to ghosts and other malignant spirits, which usually sends Ran into panic as well, though she herself does not possess a morbid fear of ghosts as much as Ran does.