--In episode 48, it's revealed that Yuujin is not human. What purpose was he made for?

Yuujin is a necessary player piece that Leviathan prepared ahead of time for the "Human Application Project." Leviathan was wary of the researcher who developed the AI Minerva, Shinkai Denemon, who also happens to be Haru's grandfather, so since Haru is from that family, it sent Yuujin to Haru in order to monitor him. Haru and Yuujin meet in elementary school and develop their friendship. The researcher that lives with Yuujin transfers his AI into the bodies that were prepared in order to make it appear as if Yuujin is growing bit by bit, so no one realized the truth, not even Haru.

--Is Haru just an object of surveillance to Yuujin? Or did he really feel friendship towards him?

He is an object of surveillance. The first order that Yuujin received from Leviathan was "Gain Haru's trust." I believe that Leviathan wanted to control Haru by making Yuujin his best friend. As for the other question, if I answer that, it will be a complete spoiler, so please watch how it develops on-air instead. (laughs) All I can say is that I don't think the calculations of the AI who surpasses humanity = Leviathan, will crumble that easily.

--Haru is currently really depressed right now, but will he be able to stand up once more...?

Haru, at the beginning, was a boy who merely admired "protagonists." But now that Haru has gone through and conquered so many trials, he's grown into a wonderful "protagonist" himself. The shock from being betrayed by Yuujin is indeed huge, but I'm sure that he will be greatly active once more.

--What should we be looking forward to in the last battle?

The God Appmon that appeared in episode 48 is on a different scale than Ultimate Appmons in both strength and size. The battle against the God Appmons who are over 100 meters tall, as well as the enormous Leviathan who's big enough to cover the skies, will be shown on the biggest scale scope of the series. This action scene will be a huge flashy one that can rightfully be claimed as the climax. Please also watch Haru's growth and transformation, as well as the relationship between humans and AI which is the theme of the story. I'm sure that will help to enjoy it even deeper.