徹頭 てっとう徹尾 てつび
tettōtetsubi

Adverb

1. thoroughly; through and through; out and out; in every way; from beginning to end; from start to finish

Yojijukugo
わたくし徹頭 てっとう徹尾 てつびあなたを支持 しじしてきました。
watashiwa tettōtetsubi anatao shiji shite kimashita
I have supported you throughout.