UPDATE Version 2.0:
Ok I redid everything from scratch. I'm much better at this now than I was when I made the first one.
The bug where Tokugawa is unable to declare war is fixed, also fixed is another bug where Oda and Tokugawa aren't actually trading even though their diplomacy says so.
Tokugawa should no longer turtle after it wipes out Imagawa(I kind of liked it that way, but better do it through CAI than a bug), and should be expected to play a larger role in the campaign.
This mod is simply making Tokugawa Oda's vassal instead of Imagawa. It works flawlessly and doe not come with any other changes.
Spoiler Alert, click show to read:
Download "Gallusmod-OdaTokugawaV2.0.rar" for the latest version.
(Remember to delete the previous version from your data folder)
-Download OdaTokugawaV2.0+1640ec for this mod combined with 1640 extended campaign mod by spartan_warrior-
-Download OdaTokugawaV2.0+monthlyturn+1640ec for this mod combined with monthly turns mod by langtutheky (updated version by Booke) (also I fixed the problem with Mori not getting the 1640 extension)-
(I made a small screwup while porting the diplomacy into the 1640 ec and monthly turn versions which left a bug unfixed.
The normal V2.0 is still perfectly OK. Just download the fixed version for extended campaign and monthly turn.)