Yuka is Yuuichi Katagiri's adoptive mother who is presumably deceased and is mainly shown sporadically in flashbacks throughout the series. Unlike Yuuichi's mentor and father figure Shiba, Yuka teaches Yuuichi that friends are "more important than money".

Play a game that costs a lot of money with your best friends! The key to clearing the game is "don't doubt your friends." However, one betrayal raises suspicion, and the game becomes a psychological warfare! Money or friends?
 
The ultimate intellectual game manga that shakes people's hearts has been born!
 
(Source: K MANGA)
 
Note: Includes three extra chapters.

High school student Katagiri Yuuichi, who values friendship above all else, enjoys a fulfilling life with his close friends Sawagiri Shiho, Mikasa Tenji, Shibe Makoto, and Kokorogi Yutori. 
 
However, after a particular incident, they're dragged into a debt repayment game. 
 
The only way to beat the "Tomodachi Game" is to not doubt their friends. Bound together by solid friendships, the game should've been easy, but– The hugely popular comic that sold over two million copies is finally becoming an anime! Will they trust or betray their precious friends? The true nature of humanity is exposed in the ultimate psychological game! 
 
(Source: Crunchyroll) 
 
Note: Premiered on Hulu and d Anime Store at 0:00 on Wednesdays, 1 hour 29 minutes ahead of Nippon TV's broadcast.

Yuka Katagiri