Just beat Ultra Odin and got Rune, but I'm too broke to upgrade him since I spent 30000 on recruiting tavern units earlier today
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Bring someone who can disarm bombs, trust me on this. Also, I originally made the assumption they were similar to the bombs the oxcesian guy in chapter 20 makes, I was really mistaken, since you can run into them and they would blow up. It's especially dangerous since he does it after zantetsuo, which reduces everyone's hp down to one, and the really dangerous thing is that next turn, when he moves he can shove you into a bomb, and you have to make sure not to be vertical because he will do breath vertical. 2 turns after the bombs, he will do life drain bringing you back down to 1 hp again and healing himself for the amount. After that he will call in the fenrir dogs, but I just went straight for him before they could do any damage to my team. Pretty awesome fight, since atm it seemed like you really have to plan ahead. I admit I did the save/load trick twice because I did not expect the bombs to explode on contact and him shoving my team into them.
Also kill the 2 birds first, they heal Odin. They will counterattack your characters to defend the other if you didn't kill them in one shot, so it's worth it to power point them when you have the chance, since it is easy to build up super meter against the boss.