盛り上がる
もりあがる · moriagaru · JLPT N1 · verb-godan
to rise
盛 — 成 (chéng, phonetic) + 皿 (vessel)
A phono-semantic compound: 皿 (a dish or vessel) gives the meaning, while 成 supplies the sound. The original sense was grain heaped into a ritual vessel as an offering, hence 'to fill' or 'contain' (chéng). From 'full to the brim' it extended to 'abundant, flourishing, prosperous' (shèng).
上 — horizontal line above a baseline
上 is an indicative character (指事): a short stroke placed above a longer reference line shows the concept of 'above' or 'up'. The earliest oracle-bone forms used two horizontal lines for this; the modern shape added a vertical stroke for clarity. The core meaning of 'upper, above, to ascend' has stayed stable for millennia.