My first thought was building Sophia, but I don't have an owl tome for her. Somehow the only owl tome I have is Blarowl. I preferably want something highly merge-able, so no 5* exclusive or seasonal if possible. The last legendary gave me a 33.333% Robin instead of Jakob or Genny, so here I am.
Yeah, I know what you mean. The only red unit with an Owl tome is Katarina, and she's a 5* exclusive for whatever reason.
Since giving Close Counter to Sophia was part of your plan, then I'd suggest holding on to your Takumi until you either get a Katarina (that you don't mind foddering off) or until Intelligent Systems releases another unit that has the skill.
Or, who knows, maybe Sophia will get a weapon refinement.
I think Sophie seems a little bit uhhhh for CC because her def is only 28 to 31. Many unit in arena can physically one kill her (I think). boey will be a good candidate for CC due to his bulk. but eh, if there's no good unit or you are still hesitant save your CC and wait for unit that is worthy for it. the skill is pretty rare nowadays.
Well, Owltome (if she's near 3 allies) would give her 6 defense, and another 6 defense for Close Defense, giving her 46 defense, and that's before her allies having skills like Drives/Spurs/Fortifies.
Sophia isn't the "most optimal" choice for Close Counter, but she's definitely a fun one.
Closest thing that comes to mind is possibly Saizo, Azama, and Boey. Boey also comes with an Owl tome if you really want that. Going off of Blue Tome users I can't find anyone other than Robin who does have that form of 29 bulk.
Though if I may, I know it goes against your desires but I personally would recommend CC on New Years Corrin due to his high bulk hitting 37 Defense after refinement+merge. Helps against the harder hitting units and makes up for his slack in Speed.
Edit: Attached the image of my NYC
Pokemon GO
Fire Emblem Heroes
Fate Grand Order
Dragonball Legends
Dragalia Lost
IV Calc
Heroes