Allying Oda as Tokugawa

I am attempting to start a domination campaign as Tokugawa in which I spend the first half of the campaign best buddies with the Oda. I'm playing Very Hard so I expect Imagawa to attack me within the first 20 turns so I have somewhere to expand, I also intend to offend Imagawa as best I can.

However I'm having trouble with gaining Oda as an ally. At the moment I've found the only way to gain peace is to destroy his army in my territory then move back to my castle and defend against his second stack. After this he will accept peace but then be destroyed by Saito within 2 turns. I'm confident that if I can make peace with him and keep him alive he will eventually become my ally. At the moment all I can think of is going to war with Saito and helping defend Owari.

Any advice?

Make Oda your vassal and if necesarry post a stack near Oda's castle.

The only problem with an ally like Oda is that they will be attacked by every neighbour and will drag you into wars in the centre of the map when you should be expanding SE along the coastal corridor.

And if you decide this isn't the time for a war with the great Ikko Ikki hordes rampaging to the north and break the alliance Oda will then attack you anyway.

Plus while an ally who is at war with the same enemy as you will get and grant automatic indefinite military access a peaceful non-ally (even a hostile one) that has a border with you will usually pay large sums for military access - at legendary I generally get 400-750 koku for the first 5 turns, 1000-1750 for the next 10 turns and 1500-2500 for 20 turns (never sell indefinite access as in 20 turns you may be able to repeat the process) - that's 3,000 to 5,000 extra koku you can make in just three turns and hugely important in the first few moves.

You may well be better off just fortifying Mikawa as fast as possible and never ever leave less than half a stack in garrison.

In legendary campaigns I've tended to avoid making alliances or vassals - instead aiming to keep the neighbouring clan trading and very friendly - currently as Mori I've been friendly with the Bessho for nearly 40 years and have used them as a buffer while I've conquered everything to the West and then went around them by sea to take Kaga, Echizen (both vital provinces for pumping out upgraded troops) and the provinces around them.

However while this may work with a western clan its unlikely that whoever holds Owari will keep it for long as it really has a magnetic attraction to every eastern and central AI faction.

One tip - exchanging a hostage (one of yours - in dozens of campaigns I've never persuaded the AI to give one up) makes a big difference to the initial negotiation.

Yeah the alliance with Oda is more of a role play thing. I'm going for historical accuracy (kinda). Probably I should just befriend them and leave them alive, the really key thing is that they are there and forging an empire. I could vassalise them but it wouldn't feel right. I don't really mind being forced into wars in central Honshu as I will be focusing on the East and Oda will form a wall between me and the West, although sometimes I may lose a trade partner.

Indeed Imagawa is a bad master - I have seen so many times that Imagawa turning against Tokugawa.
Oda is very powerful if you watch his back (east). I agree that you should befriend Oda - marriage works better than alliance as you don't have to join Oda's Wars. Oda is likely to get into trouble with Ikko-Ikki sooner or later, and you want to take Echizen-Kaga anyway.