True, Esdese would most likely find a great Teigu for Tatsumi...him just changing to another side would certainly tip the scale but what about when he returns? Then Tatsumi would be compatible with two Teigu!
Well we know that people normally can't use two Teigu at the same time, though I don't think that there would be a problem is say...Tatsumi "lost" his current one and became compatible with another. But it will probably happen later on one way or another so we'll see.
Oh I'm fully aware that Tatsumi x Esdese is a titanic...but still I really like Dere Dere Esdese so I can't help myself xD chapter 26 and 27 for example are a going to be awesome for me (except the ending of 27...though I can't read Japanese so it might not be as bad as I think).