Lithium

I don't think it's forced, I think it's slowly been building to it. Especially because chihaya is so dense and doesn't know her own feelings.

The reason why in the beginning and during the manga she always thinks of arata and has so many flashbacks to him, always sees his face in so many crucial moments and moments with strong feelings - is because he's the best and strongest at karuta in her eyes.

There's the moment when chihaya plays hyoro for the first time and she finally acknowledges him, and he says she's cold because she never has ackowledged him before because she only acknowledges strong players and views him as weaker than her. She can't say anything but "true" to that.

Then when arata finally plays taichi he has the same realisation, that he's never acknowledged him in karuta before or ever thought he could lose to taichi.

In the first instance when taichi left the club chihaya could see his strength in karuta and knew he would be back and with her on the queen stage (that declaration leans romantic for me). When taichi then played karuta with other strong players, chihaya acknowledges his strength. When chihaya became the pillar of the misuzawa club she again acknowledged taichi's strength. When taichi is over at chihaya's house he acknowledges chihaya's strength with her exceptional hearing to her mother, this moment again layers into chihaya's feelings of strength and romance (in this strength perspective it's a passionate and romantic thing to say in front of chihaya to her mother).

Throughout the series we see these themes, but I think chihaya's feeling for taichi grew stronger when she said "my dream is for taichi to reach class A". She loves him and wants to play karuta with him at the same level in the same class. Her feelings continue to grow with her unaware.

Chihaya's sense of the world and herself revolve around karuta, even her love life. So while in the beginning she always thought of aruta because he's strong in karuta, when taichi reached the same level she thinks of him more too, and that is where we see her honest feelings grow now towards taichi.

I don't think chihaya was going to end up with aruta because he was so far away, he became a godly figure of karuta in her eyes. Because she elevated him to that status it would take time to humanise him as a love interest for her, but aruta didn't have that time because he lived away.

If both taichi and aruta lived in tokyo and played karuta by chihaya's side we might have a different outcome. Aruta could see this, which is why in the last chapter he teasingly says to taichi, well if you stayed by her side at 18 I might try to stay by her side at 28. Because he knows chihaya's feelings need to develop in proximity. But obviously I don't think chihaya and aruta will ever get together now because she's committed and fallen for taichi.

Yes it may feel forced if we don't understand chihaya's feelings in this way or this perspective, but I enjoyed the slow burn aspect of it.