User blog comment:Chichiryuushintei/High School DxD BorN Episode 5 Review/@comment-26285797-20150505133335/@comment-26345952-20150506030757

ha, yeah, can't argue back there; for the most part the church trio are the ones with little development towards them, as far as I know we only have one for each and one of them: Asia on Vol. 6, Irina on Vol. 18, and Xenovia on Vol. 19.

(One can argue that Rossewisse and Ravel are other ones, but I'd say their new comers, I mean Rose didn't join until Vol. 7 and had her debut on Vol. 17; Ravel didn't "officialy" join until Vol. 10 but through a collection of her small scenes on the series so far she had a development towards him,especially on Vol. 14)

For long running caracters that have basically been there since the beginning of the series, The Church Trio have the slowest (or the least) development towards Issei (in a personal level).