Well, you are in luck because Yasuda made
a whole article on mobile in Japan for April (the financial round ups were for March).
Which, I probably don't have the time to TL before I am gone. You can probably read Japanese so you can check it out (at least I think you can read Japanese from memory).
As with any analyst, he can be wrong, though I sure hope he don't make up his numbers, at least. IIRC, he said several companies (which isn't specific beyond SE and Bamco in the article I translated) had faced general contraction in the recent quarters, but he really only raised the specific example of SE and Bamco (and for Bamco just one game)...since KT, Capcom and N1 have barely any mobile game presence.
In this new article, he has more concrete examples of COLOPL, Konami, GREE etc.
The title of the article is "Is the mobile market in Japan retracing the steps of the Pachinko market?"