Dragon Gate had a pet monkey they used as an idol that the younger wrestlers took care of. RYOMA, Tozawa, and Ono were said to be abusing the monkey. Not just kicking it but lighting firecrackers on it, choking it, throwing it, etc.. It got out to public, and RYOMA took the majority of the blame because he was the one chronicling all the abuse, photographing it, and being caught red-handed. But several students had said Tozawa and Ono abused it as well. Whether they did it because their friend did it or not, doesn't really matter. They did it, but RYOMA was the one that Dragon Gate could blame and punish and hopefully sweep everything else under the rug.
As far as I've found, Tozawa himself has never apologized for his involvement and definitely not in any meaningful way to show he learned from the abuse. It's why when Mecha said 'stuff we did 5 years ago', I had to think, 'what the fuck could you possibly have done as bad as abusing a caged up animal?' It's not like they put him in silly suits or made fun of the guy.
Araken was the whistle blower. Shingo's picture was from when the monkey had escaped and it was caught, fairly unprofessionally. But it wasn't Shingo encouraging or voyeuring the torture acts the three did to the creature before.