The ad, which was published in the June 9th Issue of the Asahi Shimbun, is a manga page drawn by the author Isayama Hajime and titled "Attack on Titan's Final Volume Announcement".
The contents show Eren as being suddenly reincarnated in Japan, but he is immediately run over by a truck and reincarnated into a video game-like parallel world. After being lambasted, with the power of a Titan Eren defeats a monster that suddenly appeared. When he makes fun of it by saying "Huh? Did I step on something?", the monster got incredibly surprised, crying aloud "Uhhhhhh".
On the page, you will also be able to read something that seems to be a title which says, "I was lambasted after being reincarnated in Japan for a moment, then I died and was reincarnated into another world. But when I turned into a titan for a bit, everyone flip-flopped and cheered me on". At the page's bottom a note saying, "The 'real' end follows".
Given that the ad looks like the well-known and intended "fake announcement" published at the end of the volume of "Attack on Titan", fans will definitely want to check out the ad page on an actual newspaper.
The final and 34th volume of "Attack on Titan" is currently on sale from June 9.
(C) Isayama Hajime / Kodansha