Not a very major character in the early part of the series but at the later half, he was significant in the plot development, where he locates Sho and the others and guides them to a new hide-out.

He was also transformed into an Experimental Zoanoid to escape from the poison injected into all captured scientists. He was able to survive only because his 3 other friends left behind their research on mutation.

Note that he did not steal it from them or anything, it was just that his luck that he was the last one to be trialed on and only his was successful where all others failed.

Toshiaki also aided the group at various times of need and actually defeated Enzyme III with the help of Aptom and Guyver III.

Sadly, in his bid to save Aptom in tha later chapters ( around hte later 140+ chapters ) he gave his life so that aptom can be revived.

My Comments
I like his Zoanoid design :) Looks very much like a guyver unit that is not evolved or something. his powers are weak but the man behind the mutation is not weak at all.
Taking on Enzyme IV is like an ant trying to crush and elephant!! This guy is no joke!! Give him something more powerful and he could do wonders.