I bet you guys that Deeply Jealous God is MC in his current state from the real world (that is minus one arm, leg and eye).
Or his girl friend who fell with him last time.
"And yet there is no explanation of why it's all Japanese language. The problem becomes more obvious when they actually bring attention to the issue, as done here."
That's for the same reason all aliens in US-made sci-fi (almost) always speak English - it would be too much of a pain for the creators otherwise.