The similarity between "to enter (入)" and "number 8 (八)" confuses me. What's the extra part on top of 八?
Not all fonts have that horizontal thing. Here are examples of the same 八 rendered with various fonts installed on my PC:
- Are hiragana letters written with their small nuances?
- How often do single dots stick to the top of kanji?
- Which kanji writing should i follow when writing on paper, digital or non-digital?
- Is there a reason why the 濁点【だくてん】（ ﾞ）are placed below the stroke at ぐ and で as opposed to the other hiragana characters?
It is a design typically used for the typeface called Minchotai (roughly equivalent to Latin serif fonts). Basically it is designed so that glyphs are closer to those written with brushes.
In typography it seems to be called 八屋根 (hachi yane), literally "eight roof". Quoting the image and text from here:
Translation: The 6 characters on the bottom right have the element called "hachi yane", which represents the starting of "migi barai" strokes (strokes going diagonally from left to right) as seen in 八 and 入.