Hiratsuka Sensei With a Smaller age gap
Hikigaya is a third year when Hiratsuka first starts teaching at Soubu High School. He is pretty much like he is in his at the start of the series but maybe without the border line incel behaviour.
Hiratsuka really helps him out and helps connect with him over similar hobbies and helps him apply himself more and strive to be successful and enjoy himself more.
These actions really touch Hikigaya and he develops a small crush on her but he knows it's something that won't come to fruition as he already knew that Hiratsuka had a boyfriend at the time. Hiratsuka here hasn't really had her love issues yet so is a lot more confident, acts a bit younger and doesn't really show any of the issues that were shown in canon.
Whilst close they weren't really close enough to keep contact after graduation. This is also in part because Hiratsuka had a boyfriend at the time so was focusing on that and Hikigaya wanted to get over his crush anyway.
Hiratsuka's teachings helps Hikigaya do well in his third year and then at college. Leaving him in a decent position in regards to work where he is earning a decent amount and doesn't need to work himself half to death to earn it either.
While Hikigaya is doing well and even has a small group of friends (though no one especially close), his romantic life isn't very good, unable to have a long lasting relationship. Now that he's getting to that age (around 26), his parents arrange a match making meeting without even asking him before doing it.
Deciding to go for it he attends the meeting only to come face to face with his former crush and Sensei that he hasn't seen in years as his partner.
"Hiratsuka Sensei..."
Hiratsuka Sensei has had her love issues now and since she's now the age she is in the actual series (or maybe a couple years older) she seems to be a bit desperate in finding a partner and is a bit different from the last time they met.
You can then go into detail about how their meeting goes and what follows it.
