Well, as always, Seira chapters are heavy... In lots of ways.
We see a side that, at least personally, didn't imagine. Seira being the "queen" of the school, being good in grades, sports and socially.
We see there WERE men that approached her, yet she didn't see them as good enough, so she kept single.... Then adulthood hit. It's something relatable. Being in a relationship is seen as normal (at least in the real world) and it's only natural to want to love and be loved, even more so to her. We see she's been putting up the effort for that "destined man" for like 20 years.
That part of her is the one that, albeit shortly, hated Masato when he rejected her. "Oh, I break my back for 20 years, study, work, take care of my appearance, and STILL you WON'T love ME?!".
Of course no matter what you do, you can't force another to love you, but it still feels somewhat unfair when you think you're doing everything "correctly" for """nothing""". Lot's of people can't deal with rejection for this exact same cause. There's no magical pattern for love, after all.
Then we see her in college, and she herself admits, she got scared. It happens, honestly. Everyone waits for the fated one, but sooner or later, if that destined one doesn't appear, you start getting scared. "What if I remain single forever", "What if my destined partner already found someone else?" "Ah, another friend got a boyfriend/girlfriend, at this pace I'll be the only one alone" and such. Scary things, let me tell you. That's why she accepts the advances of the first dumb-ass that approached, getting hurt and being unable to trust men in the process.
That's how we got chapter 1 Sierra. A woman that lost contact with her friends, works a boring job, has no hobbies, no family (that we have seen at least) and feels betrayed by the opposite gender. A true loner that gave up.
Then Masato appears, falls in love, and now is scared. She doesn't want to go back to being a loner, even recognizing herself as a loser, getting eaten away by depression. She's desperate, she's scared, she's depressed, and suddenly... A desperate chance.
"...What if I get pregnant? He's a good guy, so he'll take responsabiliy..." "It's not my fault after all"
This plan has no head nor tail, yet she's too emotional to notice the horrid decline she's suffering. She can't rationalize long term planning anymore. Sierra needs to stop feeling like dirt, a fool, a woman that got used, a psycho... And all that can be brushed aside by a "Let's get together" from Masato... And she's going to get it one way or the other.
Finally (thanks for reading btw, I know there's some that been reading my comments in every chapter, love you guys) I said it once and I'll say it again. This manga is amazing. It NAILS to a T everything romance related. It's an adult story, not because the characters are adults, but because they have adults feelings. And adult feelings are, in a word, complicated.
What will society think, what will their family think, what I lived before this relationship and what did they go through, how will things work out, What if X happens, how will this affect my work/studies, what if they say no... Normal questions for the ones searching love. I like the constant anxiety the girls (and FINALLY Masato) go through. You may think "Oh, it's just getting a boyfriend/girlfriend" But for the people involved, that means their world. The one person they want to spend the rest of their LIFE with. Absolute banger, read all the chapter covering my mouth. 9/10.