A line on the last page of “Spring Cherry Blossoms” is different from the original. (And no, I didn’t change it.) Sho’s line in the first panel is “We won’t commit 心中 (shinjuu – lovers’ suicide/double suicide), so please don’t worry.” in the original.
Japan has had a long tradition of lovers committing suicide when they couldn’t be united in this life, so they could at least be united in the afterlife. Incidents of shinjuu sharply increased the Edo era, so much that a decree was issued to ban it.
In the Taisho era (which is when this story takes place), shinjuu was still not uncommon, and there were famous cases of celebrities committing shinjuu. So if Sho and Takao couldn’t obtain their parents’ permission to get married, shinjuu would have been the logical way out.