Can Sempai be used to address a student of the same year/age

Question

I've been working on a script for a Visual Novel, in it one of the heroine's Sakura address's the main hero Talavaliau (Tala for short) as Sempai because she has a crush on him and can't bring herself to actually call him by his name even with honorifics but also as a sign of respect for his nature

i base this on a number of anime/manga/books/games i have seen where a younger girl addresses an older crush as sempai and in most cases their just a class year's difference or have a year gap between their age

i know that sempai is used as a form of respect for younger students to address older students however in my script, Tala ends up being reassigned into Sakura's class so they are in the same year in the school, Tala's and Sakua's age are the same but Tala's birthday falls on the same day as his foster sister (he no longer remembers his real birth date and uses the day he was saved/adopted) which is only 1 month before Sakura's

so i am wondering if Sempai can be used to address a student of the same year/age or if i should use another term which doesn't involve using a person's name

Answer 1

It can refer simply to age, but especially in the context of school it will refer to someone in a grade above you. It's a similar thing in work or other organizations: your 先輩 are the ones who came first and outrank you. Outside of a strict hierarchy (like school or work) I think it just refers to the idea of someone being older, as in 彼は私の5年先輩です。 (He is five years my senior.) It may also be worth noting that dictionary entries tend to roll up the idea of simply being born first into the same definition as seniority in academia or in arts, so this may be more of a reference to someone who is more wise or knowledgeable rather than just being older. For example I don't think you really refer to elderly people as senpai.

Technically your classmate is your 同輩 (douhai), although as istrasci (and formerly snailboat) reminds us this term is not the most common, and instead 同級生 or other more common terms would be used (emphasis that this describes the relationship, not the term you would use to talk to them). These people would be addressed with kun/chan/san/whatever else. When in doubt, just stick within the established hierarchy. As a (pro?)noun used to address people, though, you have senpai but not much else.

Answer 2

In context of some organization, Senpai means came earlier and is not necessarily based on age.

One can call younger people 'Senpai' in corporation.

Answer 3

Yes, "sempai" can be used to address a student of the same age, or even possibly someone of the same year, if he/she entered the group before you (for example, if he/she joined the club in the spring semester and you joined in the fall semester).

Adapted from part of my answer to a question on Anime & Manga SE here:

Sempai (「先輩」) are upperclassmen in some sense, to whom a Japanese person will always be kouhai (「後輩」, underclassmen) throughout their lives after graduation.

Sempai are often older, but not always: more important than age is the person’s year in school OR number of years in the shared 部活／サークル／チーム (bukatsu/circle/team = student organization), アルバイト (arubaito = part-time job), 会社 (kaisha = company), ボランティア活動 (borantia katsudou = volunteering group), etc. at the time that the kouhai enters said school, club, team, or company.

For example:

• If you enter university as a freshman and meet a sophomore who is your own age, he/she is automatically your sempai by virtue of being a grade ahead of you.
• Even if you had graduated from the same class at the same high school and are the same age, if you had 浪人した (rouninshita = taken a year off after failing a college entrance exam and attending 予備校 [yobikou = cram school specifically for entering university]) and he/she didn't, now he/she is your sempai from college onwards.
• I'm a member of the manga student group at my university in Japan, and we all call each other by “-san.” Even though they're all younger than me (since I'm a grad student and they're undergrads), it would be totally inappropriate for me to start calling them in 呼び捨て (yobisute = without a respectful name suffix) because they either 1) are my sempai in terms of number of years of membership in the club, or 2) they entered the club at the same time as me.
• Even if you have not seen your sempai in decades and you are now both middle-aged and working at different companies of equal repute, when you meet again he/she is still your superior to whom you must look up to, defer to, and serve; there is no evening-out of level in Japanese sempai/kouhai culture. There is no analogous system to this in Western culture.

Answer 4

A classmate would never call another sempai. That is reserved for people in the year(s) above you, or people who began your job before you. (You say "just one year apart" but that one year makes a big difference and is important.) In a class at school, everyone is equal, regardless of their actual birth date. She would call him [name]-kun or [name] with no honorific if they were close. If they met for the first time outside school, it would still be ridiculous for her to use sempai because that's only for school/work. If you want her to use something besides his name to his face, it has to be a teasing nickname, like Mamoru would call Usagi "Odango-atama" in Sailormoon.