I understood what you meant by your message. The meaning of ﾞ and ﾟ in Katakana. ﾞ(double dots, I just wonder if your computer show the mark properly) make the sound to a voiced sound. カキクケコ(ka,ki,ku,ke,ko) become ガギグゲゴ(ga,gi,gu,ge,go) サシスセソ(sa,shi,su,se,so) become ザジズゼゾ(za,zi,zu,ze,zo) タチツテト(ta,chi,tsu,te,to) become ダヂヅデド(da,dzi, zu,de,do) ハヒフヘホ(ha,hi,hu,he,ho) become バビブベボ(ba,bi,bu,be,bo) You may think the correspondence between h and b is strange. Actually it should be p and b phonetically. The ancient pronunciation of ハヒフヘホ is considered as pha,phi,phu,phe,pho. But they changed into ha,hi,hu,he,ho. That's why Japanese people think the voiced sound of H is B. And for expressing the sound 'P', the small round mark ﾟ　was introduced. ハヒフヘホ(ha,hi,hu,he,ho) バビブベボ(ba,bi,bu,be,bo) パピプペポ(pa,pi,pu,pe,po)

Katakana is a phonetic writing system. The characters don't have meaning. Can you explain what is your problem?