Lets try to get this thread on topic again!
Japan is in the technological terms, one of the most developed nations and closer ties to them would be very interesting. So in what fields could we use their knowledge?
As I said in some other threads before, Japan and India share imo the the same major threat, the Chinese sub fleet! To defend itself against them, Japan don't rely just on their subs, frigats and corvetts, they also use helicopter carrier with ASW capabilities, as well as shore based MPA like these:
Hyuga class
Sikorsky S60J
Kawasaki XP-1
IN already ordered P8I long range MPA, but these helicopter carriers would be interesting, because the latest news say IN is also interested in Mistral class LHDs.
These Hyuga class carriers have nearly the same size and are designed to carry helicopters and troops, the only difference is the lack of a well deck, to carry beach landing vehicles. Japan build LHDs before and can look back at experience in carrier development till the world wars, so a co-development for LHDs, or helicopter carrier would be very useful for both countries.
Also these Sikorsky S60J are only build under licence starting 20 years ago and HAL is searching for a foreign partner to develop a new medium size helicopter. One reason for this was, that IN rejected the Dhruv as an ASW helicopter for the carriers and frigats, because it offers not enough range. So a combined medium size helicopter development, especially for the ASW role could be interesting too!
But it gets even better!
Japan also have plans to develop a 5. gen stealth fighter with similar design, size and features as our MCA like TVC:
Mitsubishi ATD-X
Although this project could already be too far, because first flight is already planed for 2014, some sources say even 2011. On the other hand Japan is still asking for F22, F35 and negotiating EF, or F15 SE, so the reports are not really clear, however this could be a field for defense cooperations with India too.
These are only some suggestions of me, maybe you guys can add some more.