Source: Kankou (US forums)
So, you think the Japanese projected only silly riveted tankettes? Check this out:
This is a 100 ton heavy tank, designed by Hideo Iwakuro, known as the "Iwakuro tank". Armed with a 105mm cannon. Twice as big as the KV-1, this monster is speculated (with high probability) to appear around tier 6 in the Japanese heavy line (another version with a 150mm cannon was confirmed by SerB also). Do not mistake it however with the O-I, this is NOT the O-I, that came later.
Edit: Kankou provided the armor values and cannon info:
75mm front, 35mm sides (with possibly another 75mm + 35mm plate bolted on it, eg. 150mm front, 70mm sides - but I doubt that will make it to tier 5-6)
Cannon: Type 92, 120mm penetration at 100m
And this is lowtier stuff. Imagine what monsters await us around tier 10... :)