Shiki must still get in range, aim, and strike the target himself, which is not a trivial task against the kind of enemies he faces. He ignores his best friend Aech. He even admits it during their first online chat, telling her:
ho want my big tits
This mature clearly loved that veiny penis. Couldn't get enough of it even after she got a big payload for her troubles. She continued to suck his cock after. She's a keeper.