It was reported this weekend that Yokoyama Yu's mother passed away recently. From the news report it was very sudden as she was not suffering from any known illness and is suspected to be from a heart attack.
Yokoyama has decided to not cancel any of this work obligations so he will still perform his solo concerts and be part of the promotion for Kanjani8's upcoming single, Wonderful World.
Arama They Didn't entry. (Japanese & English)
Like everyone else I feel like I need to express my condolences for him and his two brothers for their loss. She was a single mother and worked hard to raise her children so I'm sure the loss is great for them. Though I also understand why he would still want to continue to work other than just not wanting to disappoint his fans, as it gives him something to focus on other than the loss. I truly wish him well and hope the love and support of his friends and fans will help him get through it.