Oniichan

Have any of you ever questioned why its oniichan or oneechan and not imotochan or ototochan? I'm just curious because of the suffix title thing being added to the end lol

There's nothing weird about it. It's same as in English where we say bro or sis instead of brother or sister. Just little traits of the colloquial language.

Imoto and ototo are for younger siblings, but in Japan, you just call your younger sibling by their name. Oh, I misread the question. The reason there is no "san" at the end like Oniisan, is because you don't need the respectfulness when talking to the younger sibling... if that makes sense.