Sumire Koike

Sumire Koike (小池すみれ, Koike Sumire) was Himeko's friend in elementary school and is actually unaware of Himeko's time as the Onihime. Her sending Himeko a letter is ultimately what prompts the Sket Dan to visit her in Osaka for Golden Week.

Appearance
When Sumire was younger, she wore glasses.

Trouble Travel
Sumire sends a letter to Himeko, suggesting that the latter visit Osaka for Golden Week. As a result, Sumire finds herself hostess to the Sket Dan trio. During a dinner conversation between the girls, Sumire's cellphone rings and Himeko notes both the name on the caller ID and the distraught expression on her friend's face. She ultimately convinces Sumire to explain the situation. Evidently, two years ago, Sumire was approached by and started dating Tsune, but they broke up after about 3 months when he became a delinquent. Even though they had broken up, he continued to send her text messages, which she figured she would just ignore in the hopes that he would give up and leave her be. As Sumire quickly leaves the table to go the bathroom, she drops her phone and Himeko reads the text message on the screen - which is asking Sumire for a hefty money loan.

When Sumire returns, the girls resume their meal and chat. However, Sumire is unaware that Himeko had answered a call from Tsune during her absence. The girls part ways for the evening, but, later that night, Sumire receives a phone call from Bossun. She is surprised to learn that Himeko has yet to return to the hotel where the Sket Dan are staying. She comes by so she, Bossun and Switch can puzzle through the situation and suddenly recalls how she had left her cellphone on the table while in the bathroom. Reading the text message therein, she guesses that Himeko must have seen it as well. The trio soon realize that Himeko must have answered a call from Tsune and subsequently went to confront him, much to Sumire's dismay. Bossun figures out where the meeting was set to take place and he and Switch set out to rescue Himeko, telling Sumire to stay behind and wait because she is technically also in danger.

After the boys' efforts prove successful and they manage to rescue Himeko, Sumire sees the trio off when they head back home.

Etymology

 * Sumire's surname Koike means "small" (小) (ko) and "pool, pond" (池) (ike).